Acceptance to online publication – Why is everybody I know faster than average?
From personal experience, I can say that while the usual time from acceptance to online publication may be quite short (for a good journal), there are occasionally situations where the process takes a lot longer.  This probably pushes the mean time interval up quite a bit.

Over the last five years, I have published a couple dozen papers, and for most of them, the time lag between their acceptance and their appearance online was just two or three weeks.  However, for three of those papers, the time was quite a bit longer--a matter of months instead.

The reasons for this varied.  In one case, the copy editor raised some questions about my wording, and the paper passed back and forth between me and the journal several times before both sides were satisfied with the way the terminology was used.  For the second paper, the proof contained a serious error in one of the equations, which took three more rounds of proofing to get corrected.  (Every time I explained what needed to be changed, they messed up something else; it was frustrating.)  In each of these cases, it would take a couple weeks for the editorial staff to make the changes, generate a new proof, and send it to me.  When you need to go through four proofs, that can stretch the process to two months.

I don't know why the third paper took three or four times as long as usual; it just did.  Presumably there was some difficulty at the editorial office, but I never pressed them to find out what it was.

I try very hard to submit very carefully composed and edited manuscripts, and I encountered a few slow-moving manuscripts.  I know there are a fair number of people whose manuscripts routinely need quite a bit more editing work than mine.  Mostly, I think this is because the authors are not native English speakers.  However, whatever the reason, there are going to be a nontrivial number of papers that need to be sent back and forth between the authors and the editorial office multiple times.  These give the distribution of time delays a long tail and probably stretch the mean waiting time out significantly.