Early morning travel time to Heathrow from London Victoria

If you are close to Victoria station then take the tube from there. Why go to Paddington and pay the price for the Express? My guess is that it would take about the same time. For me 6 might be a little tight and I would try 5.30. But I am the type that would rather be an hour early than one minute early.

I agree with Frank, why go way out of your way to get to Paddington, just hop on the Piccadilly line, or even the coaches from Victoria Coach Station.

Or take the direct coach from Victoria to Heathrow. Going via Paddington and Heathrow express sounds like a detour.

From your other posts it looks like you are traveling with 'kids'.

Having to do a 4- 430AM wake up, I would consider going to an airport hotel the last night after dinner in London.

Wrangling kids and luggage that early seems to be cruel and unusual punishment ( for everyone)

We have discounted tickets on the HEX with the kids traveling for free which is why we wanted to do that in addition to the ride time being shorter than other options (about 18 mins from Victoria to Paddington and then 15 minutes on the HEX) versus Elizabeth Line, Picadilly Line, or National Express saying 45-60 mins). Our kids are teens, so other than whining (!) we don't have to haul little ones. Our flat is already booked for the last night we're there and when I looked at hotels at Heathrow before booking our flat, the rooms were insanely expensive.

As you have the situation as described you might as well use the HEX tickets, much as it is a real route deviation but I would worry about a 6am departure. I would want 5.30am.
However there have been a lot of issues recently on the lines out of Paddington, due to weather and the HS2 building work.

Just as you leave it is best to check train running data on TfL or whatever tools you use, like Citymapper, and be prepared to pivot to the Tube all the way if need be.

There is a curious service gap from 5am to 7am on the national express bus so that isn't an option.

There are budget hotels at Heathrow, like Premier Inn's. It is not hugely uncommon to find them under £50 a room, but very frequently £50 to £100. But you have what you have now. Holiday Inn Express is another budget chain which may have served it's purpose for you at Heathrow.

Eighteen minute to Paddington, 15 minutes to Heathrow.

Now add the wait for the train at Victoria, the walk from the tube lines at Paddington to the HEX lines, and the wait for the next HEX train.

Everyone seems to forget that part when they run to take the HEX train because it's only 15 minutes.

Sort of like the way Ryanair prices flights. It may only be 10 GBP for the fare but by the time you add the extras, it's a lot more.

...when I looked at hotels at Heathrow before booking our flat, the rooms were insanely expensive.

They do have some budget hotels at Heathrow. I booked the Holiday Inn Express at Terminal 4 for my last night, and only paid £98 for the night. There is also a Crowne Plaza and a Premier Inn, which would have very reasonable prices as well. I don't know what terminal you're flying out of, but any of those hotels will get to a different terminal if needed.

Simply take the £11.50 National Bus 444 at 7:30 a.m. from the Victoria Coach Station directly to Heathrow Airport. It's just under 50 minutes.

Don't you need to be at the airport 3 hours prior to the flight? I certainly wouldn't leave later than six which really doesn't give much wiggle room for any irregularities. I'd vote with Frank and Stuart for at least a 5:30 start.

Perhaps you got a good deal on accommodation in a flat (and maybe not cancellable) whereas a hotel would require 2 rooms.

I'm usually nervous just a few miles from the airport---on pins and needles until I'm in the Uber to the airport. . I'd vote with Frank and Stuart for at least a 5:30 start.