It's early to frost seed clover. You will likely be fine though- seed is tough. Ideally, another month on clover to frost seed.
Switchgrass is another animal though- you can do that anytime, switchgrass has a hard seed coat that's difficult to stratify. I'll probably seed some switch anytime now and wait on some clover about 3-4 more weeks.
Like I said though- if you did it already, you'll likely be ok