Will thinset be damaged if it gets wet after drying 18 hours?
Regarding strength, what's done is done.  I wouldn't worry a minute about it and certainly would not start taking up the tile in the off chance that somehow the mortar has been weakened.

In fact it can be helpful to keep mortar/cement/concrete damp for an extended period.

The spilled water does put an additional temporary moisture load on any wooden substructure, but again, this would be negligible in light of the original water content of the mortar.