What's your routine at home like? Is it the same as at daycare? & what time does he WU & go to bed? Are you having any NW's?
30min naps are usually OT for us.
Not got any personal experience of this (DS starts his induction sessions at daycare tomorrow
Do you think maybe it could be that he's so worn out from daycare (b/c its so exciting/stimulating etc) that he needs a bit extra sleep on the days he's at home? I know my friend had this with her LO when he started daycare. He would take naps there, but never as much as he does at home & so he would get that worn out that the following day when he's at home, he'd need an earlier & longer AM nap just to catch up a bit.