You may try 2 or 3 a day if you like. If a boot doesn't work don't suffer. Come in and take another pair. Remember that 2 days of demo will apply toward purchase. Often uneven pressure that you feel in the shop will resolve in skiing.
Ski boots have mechanical characteristics that can impose things on a skier.
These may appear as a fit problem in a boot that fit well initially. Patience is crucial, for you and the boot fitter. Skiing is the best way to figure it out. Don't be shy about asking questions and making comments. Prices and availability are subject to change without notice.