NO idea where else to put this - changing poo time?

[BertieBotts]

This is going to sound like a ridiculous question, but DS who is 15 months old keeps doing a poo every night at about 11-12pm - it is playing havoc with his sleeping, because he won't go to sleep for the night until it is done, he will have about a 3 hour nap, wake up and be generally unsettled, poo and then be easier to settle down again.

Is there anything I can do to, erm, encourage him to produce during the day instead?? He used to be fairly regular and had one in the mornings between his breakfast and his nap, but not any more

I know it is a strange request but any ideas welcome!

Does he do much in the way of running about in the evening? Just wondering if a good run around or activity might get his bowels moving a bit earlier on? Good fibre-rich tea and then a walk maybe?
Can't think of anything else really. I know what you mean about awkward timings, ds3 was going regularly at about 9.30am which was great and I toyed with potty training but he was a bit young but since then he has started being completely random with his dumping time so I wish I'd just gone for it when I knew when he would need to go IYKWIM!
Sorry can't help more than that.

I wil watch this thread with interest as LD dd age 4 always poos at 5am and then it is wake up time,lol