can a puppy training session be too long?

So Archie is just three months and still needs one more set of shots before he can really get out an about. For now I just take him out to the yard and very short walk along the sidewalk outside the house. This morning I done a fairly long training session with him teaching him off, sit, watch me and a little recall work mixed in. He loved it and caught on very quickly and he just kept wanting to do more. The great thing was it tired him out. I was thinking of uping the training sessions until we can exercise him properly. How long is too long for a session or am I good to go as long as he is willing? I'm sure this will be the first of many questions as I have had dogs before but never a puppy.