There is probably a large overlap; as noted in the first RFC for Timmy, both efforts happened roughly around the same time. Timere initial motivation is, AFAIK, to be a time reasoning library, while Timmy is “just” a higher level / safer interface on top of ptime with additional calendaring features such as ISO weeks and DST, which can influence some design decision.
For instance, the sole true initial motivation that sprouted Timmy was to be uncompromisingly safe wrt. the timezone, because we had one too many bug due to a forgotten optional timezone argument. Hence timezone is never optional and always enforced in Timmy, while I don’t think it’s the case in Timere. But indeed I think anything Timmy can do, Timere also can.