I have not put the hard top on for years now, so the soft top is on/up most of the time in the winter. In the summer, there are times when I leave the soft top down for extended periods (the car is garaged, and so no need to put the top up when I put the car away). In order to avoid the curls, I always make sure it goes into the well with the corners tucked down. Even after having sat in the well for, say, a month, I never have noticed creases that stay in for any length of time (as in hours).
Now there have been winters in the past when I have put the hard top on, meaning the soft top sat in its well for months, and also then I never noticed creases forming.
Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic