Depends on your level of conditioning to exercise and on how many exercises you are doing for a specific body part. I usually train 3-5 different lifts in a session. You may be using more. Sometimes I'll do a session where I do only a single exercise, as is often the case with clean and jerks -- these are pretty much a full-body exercise all on their own.
For a squat session during 5s I'll do at least 3 x 5 but that will be the only leg work I do that session. Often I'll shoot for a particular rep total; so if I'm going for 20 reps during 5s that'll be 4 sets. For the first week of 5s I will be able to do 4 x 5 without too much trouble, but during the second week I might have to do 2 x 5 + 4, 3, 3 to get my 20 reps. If I feel like my fatigue levels are starting to hurt my strength recovery between sessions, I'll reduce the number of reps a bit -- perhaps down to 15. During the post 5s when the loads are at their heaviest (>=5RM) I would still try to keep my reps up to 15 if possible. To accomplish that I'll usually do 5 x 3.
This may not suit you. It all depends on your level of conditioning and the number of exercises you are performing.
If one set provides enough of a growth stimulus during 5s then that's great. Run with that while it lasts!
A general guide would be to do 1-2 x 15 for 15s, 2-3 x 10 for 10s, and 3-5 x 5 for 5s. Something in that range will suit most folks. For post-5s dropping to triples allows you to get the same rep total with the added advantage of reducing overall fatigue.
There are lots of ways to play with the variables but it's a good idea to do a few cycles with a level of volume that you feel comfortable with and that doesn't overly fatigue you as the cycle progresses.