How soon do we need to reserve sleeper train from Krakow to Prague?

That night train seems to make 8 stops between midnight and its 6:15 AM arrival time in Krakow. A lot of people--even assuming they can get to sleep on the train at all--wake up every time it stops due to the braking, station noise and acceleration. It sounds like a way to save a day, but it may just give you a day like your initial arrival day in Europe, when you are too sleep-deprived to do much. And if you crash at 2 PM or 3 PM, you may feel sort of jetlagged the next day.

You could instead take a very early or quite late train that would allow you to sleep in a real bed and leave you a few hours in either Prague or Krakow on your travel day.

And, does anyone have experience with the reservations agency Poltrain?

You may be referring to PolRail (Jeffrey Dobek, https://www.polrail.com/en) …?

I used PolRail to purchase my reservation on a sleeper car from Krakow to Prague this past October.

Experience with PolRail: perfect and professional in every way. I read many (all positive) reviews of the company before deciding to use them to book my advance fare when the 60-day window opened. They were very responsive when I had enquiries, including very prompt weekend responses. They were very helpful in presenting and pricing my options. I decided to have my tickets sent to my hotel. I provided them with the hotel details, alerted the hotel to expect them, and the packet arrived a few days in advance of my stay - exactly as planned. Everything was in order with the ticket, including the sleeper compartment.

Experience with the night train: I do not sleep very well on airplanes. I slept soundly on the train - even with all the overnight stops. For me, the motion of the train is relaxing. I absolutely LOVED everything about the experience of the night train and count it among the adventures of my trip! (I do realize I am in a minority with this perspective.)

Disclaimers: I grew up sleeping in our family motor home (while we drove) on vacations. And my grandmother lived a few blocks from the train tracks. The whistle of trains and the motion of the train are nostalgic and comforting to me, not sleep-disrupting at all. Final disclaimer, I also took cold meds, which might have helped :-)

How soon do we need to reserve sleeper train from Krakow to Prague?

Jeffrey Dobek at PolRail will be able to give you better availability information. I chose to book as soon as the 60-day window opened to be sure I got the type of sleeper car I wanted. If you're buying 1 or 2 berths in a shared car, you probably don't need to be as concerned about availability as you would if you are buying (let's say) a 2-berth sleeper with en-suite WC/shower, of which there will be fewer.

And of course the advance purchase fares are cheaper.

Thanks, everyone! We are choosing the sleeper train as an adventure, and we are aware that we may arrive in Prague with a renewed case of jet lag. We have always wanted to try this.

You might find you have a wonderful time! I LOVE night trains...with a private compartment. We take them on purpose and as often as we can. On the other hand, I can't sleep on airplanes. Have a great time!

I reserve my compartment when I buy the tickets.

Take the night train, you save time, stretch out your traveling time, and look around who is on board.

I'll bet they are all locals, maybe an Asian tourist here or there. Almost every single night train I've taken from 2009 to last summer, the passengers were 99% German. The other 1%...Asian (a few), in this case Korean and Chinese), one US family, (literally, the only Americans I ran into), Russian, Italian, other continental European.

Keep in mind that not every one gets jet lag, ..I don't, unless you are certain of that pertaining to you. No problem sleeping on the train.