We will be arriving in Istanbul for day and a half

Istanbul is not Disneyland.

Yes you can see but maybe not appreciate all of the above during your time frame.

If memory serves The Grand Market closes at 7pm every night

Suggest you research each place’s websites for open and closing times.

Remember no bare shoulders and wear a head scarf inside Blue Mosque

No, I don't think you can do it all in one day. The Topkapi Palace I would say is at least half a day alone - it's a big site. The Blue Mosque (Sultanahmet Mosque) is smaller and the Hagia Sofia is somewhere in between in terms of size, but I wouldn't aim to do too much in one day. As noted make sure you're appropriately dressed for the mosques, head, shoulders, elbows and knees covered (you can rent/borrow covering, but better to bring your own).

Note that the Blue Mosque and Hagia Sofia are closed during prayer times, which will limit when you visit.

You certainly shouldn't be trying to squeeze more in, unless you're just ticking things off a list.

Istanbul is a safe city- no reason to be concerned about safety.

I found the air inside the Grand Bazaar very unpleasantly smoky the afternoon I went there. It has limited openings, so the secondhand smoke apparently builds up as the day goes on. It's supposedly a non-smoking area, and it seemed to me customers were pretty much adhering to that prohibition. Many of the stallholders were ignoring it. I hope to return to Istanbul, which is a fascinating city. If I decide to go the bazaar again, I will do so early in the morning in hopes of acceptable air quality.

One could spend just about the entire day at Topkapi Palace. There is a lot to see there. Personally, I'd prioritize it over the bazaar, but I confess to no being a big-time shopper.

I am a little more optimistic, but I would still consider dropping one from the list, and for me that would be the Blue Mosque. But more importantly, I wouldn't do it without hiring a guide for the day, so it's done efficiently, and so you have someone along that can explain what you are seeing and to provide a little local color.

It would be extremely rushed and I would advise against your plan as it doesn't give justice to the sites in such a limited timeframe. I understand the desire to try and see as much as you can but it would simply be a checklist that you gain very little from.

Of all the sites that you're interested in I would suggest the Grand Bazaar could be scrubbed off the list as you're limited for time. Yes it's an interesting place but ultimately it's just a large indoor (and spreading outdoors) market selling predominantly fake designer goods and tourist trinkets. Admittedly a lot of the goods are actually well made so if you're interested in buying some fake goods at good prices then the place is for you otherwise I'd give it a miss. As Acraven pointed out it is very smoky inside with many vendors smoking and it can become unpleasantly oppressive.

As for squeezing in something in the morning of the 21st, what time is your flight and what airport are you flying from? I've flown from both airports and they're very big with multiple security checks. Transfer times from old Istanbul to either airport can take almost an hour via road due to heavy traffic. Some airlines board quite early, Turkish Airlines often start boarding an hour before departure and on my most recent flight I had to undergo an additional bag and body search at the gate so it's advisable to get to the airport at a minimum of three hours before departure. If you want to visit a site on the 21st then it'll have to be early and ideally with a ticket that skips the lines.

Regarding safety, Istanbul felt very safe to me at all times of the day. It's a very busy city with tourists and locals out and about until late and there is a large police presence pretty much everywhere.

Assuming you mean October? Are you flying in on the 19th (jet lagged?), or on a cruise ship? Where are you staying? Knowing these things helps with plotting out an efficient itinerary.

As noted already, it takes a minimum of an hour to get to the airport, and if you're leaving from IST you should arrive 3 hours ahead, so you need to leave central Istanbul at least 4 hours before your flight. Depending on your flight, that may eliminate any activities on the 21st.

Here are the prayer times for Istanbul in October, which will affect your visit to the Blue Mosque: https://timesprayer.com/en/list-prayer-in-istanbul-2025-10.html The mosque closes about 30-45 minutes before and after each prayer time. In my opinion it's best to go in the morning just after the second prayer time. Unlike Mr. E, I think this mosque is well worth visiting and could be seen on the morning you leave depending on the location of your hotel and when you need to go to the airport.

Topkapi palace is closed on Tuesdays so you cannot "squeeze" that in on your departure day (and I wouldn't, in any case). I would also skip the Grand Bazaar as I found it claustrophobic and chaotic.

CL, i didn't say it wasn't worth visiting. I'm not sure where you read that. I did say, short on time, it's the one I would skip. But to be honest, with a guide, I suspect a pretty good exposure of everything on the list could be had. Especially the Bazaar.

I also reject the notion that not seeing something is better than not seeing it to the degree of depth and sofistication demanded by those with all the time in the world do. But sometimes you do max out and i am afraid without a good guude you will max out on this trip. Heck, try. Your list are the icons of Istanbul. Give them what ever time you have .... decide on the Bazaar after you have been in it an hour.

Funnily enough i quite enjoyed the grand bazaar, and didn't find it chaotic in the slightest. We bought a few nice souvenirs, had a good lunch and enjoyed it. I do agree though that the OP has only very limited time, and something would ha e to give - based on that I'd prioritise the mosques and Topkapi Palace.

I did too which is why I said go for an hour, then decide.

I just looked at the package tours on Viator and Get Your Guide. Heck, it will be a long day, but you can do it all with a guide and I dont think you would have any regrets.

Thank you all for your comments and advice. It will certainly be a hekp in planning our short stay in Istanbul