L.B.
Hi H.,
I don't really think there is a recommended time limit. My 21 month old LOVES bathtime too so I just let her stay in there until the water starts getting uncomfortable/cool (although she would stay longer if allowed). Your little one may be too young right now, but when they get older, the longer the bathtime the better...thats when I catch up on my reading! The only thing I do recommend is letting him play first then bathe him so that he is not sitting in the soapy water (especially important for little girls).
-Leanne