You shouldn't have a problem if they send you mature buds that are fresh enough. When you select buds, you want the oldest of this year's growth, so closer to the growth collar than the tip. If you look under the petiole, you can usually see the bud, although different varieties vary wildly in size. One I remember in particular from last year is Ashmead's Kernal--it has dark, almost black buds, which were larger than most of the other varieties. I would water the trees (if you can) if you haven't had the huge rains this year that most have. It is very important to have the bark slipping, and is night and day between "kind of" slipping and slipping. Take the sliver of wood off the bud before you insert it, and most importantly (in my mind), t-bud only onto smaller rootstock/branches, e.g. smaller than your ring finger or so. This has made the most difference for me. As far as timing, you need to do it early enough that they heal up/harden off before major frost, but late enough that the buds are mature. At my place (Zone 5a/b), that seems to be the first or second week of August. I guess your decision on when to graft will be whenever they send you the budwood. I can't imagine it keeps for a long time like dormant scions will. Good luck and keep us posted.
