There is a small "spin up" time to get everything hot and hot water pouring out. This is pretty minimal IMHO, and dwarfed by the amount of time it takes to get cold water flushed out of the pipes. Recirculating systems exist to prevent this problem- for tank/tankless systems- but according to some have drawbacks around increasing wear on your pipes.

I have a natural gas tankless system and find this to be a non-issue.