Please study everyday at your own pace, even if it is only for five or ten minutes at a time, and without pushing yourself too hard.

Without becoming tired. Study while you are alert and it is enjoyable. When it is no longer enjoyable (as enjoyable as studying can be), then stop. The time this takes will differ from person to person, from about half an hour to an hour. Some may even go two hours without feeling as if it is too much, but that would be rare.

Hmmm, It is a little confusing.. I would say "Please study every day AT your own pace" And do you mean stretching as in exerting yourself or actually physically stretching? If you mean exerting yourself then "without pushing yourself too hard" or "without stretching yourself too much" is fine. When you say "if it is only for 5 or 10 minutes" are you trying to say that they won't over exert themselves it is only 5 to 10 minutes or suggesting the not overexert themselves by stretching every 5 to 10 minutes?