mantra cry - every one's lo is a bit different, but the key is that it does not escalate, and is usually very rhythmic (it will have a beat-like quality to it). If it's his mantra cry, don't go in, he is trying to soothe himself. If it escalates or breaks rhythm, that's when to go it, which it looks like you're doing. Do you try pat/shh from there? Does he have a lovey (a stuff animal or something)? I don't know anything about dummy weaning, so if regression is normal, then I"m guessing you just have to ride it out - but you may want to post a thread on the props board.
A time - yes, it is very common for the first A time to be shorter than the rest of the day. My dd's morning A time was always about 20 min shorter, until just the last month, now they're about the same.. It seems odd to me that your dd's would be an hour different, but if his morning nap is longer than 45 min, then I'd keep the A time as is. Then maybe just try to push the next A time a bit - I'd only do 10 or 15 at a time though.
HTH
michelle