On the GOP side…..
I had thought that Ryan might announce that he's out as early as November, in order to clear the way for the W&M chairmanship, but it sounds like he might not believe that's necessary. So actually, he might be one of the last to declare….waiting on the sidelines and not likely to run, but possibly jumping in in the summer of 2015 if he changes his mind.
It looks like Bolton, Jindal, and Portman (if he runs) might be among the first to announce exploratory committees after the midterms, perhaps some time in the November-January timeframe. Bush also says that he wants to decide, one way or the other, by the end of the year. Perry will probably announce at least an exploratory committee right after he leaves office in January.
After, that, the next group to announce would be Carson, Cruz, Paul, Rubio, and Santorum (not necessarily in that order), perhaps around February-April or so. Possible complication for Paul is the fact that running for both senate and president at the same time seems to be prohibited by Kentucky law, so he might try to work out a loophole before he launches his campaign.
Christie, Pence, and Walker (assuming his reelection, which might not happen) will probably be a bit later, but not too late, simply because running for president as a sitting governor is trickier than doing so as a sitting Senator (in principle, this should apply to Jindal too, but we have
this). Perhaps late April or May for them. Not sure if Pence is legitimately interested, so maybe he puts it off a bit longer. Huckabee probably procrastinates until May, and then decides not to run, like last time.
On the Democratic side, if Clinton runs, she announces an exploratory committee in January or February, simply because delaying beyond that puts any other potential candidates on the spot. Not sure if anyone significant runs against her or not. I don't think O'Malley will. I guess Sanders is her most likely opponent, and not sure if he'd be in a hurry to formally declare. He might wait and see if any other challengers to Clinton from the left emerge first. On the other hand, if he's going to run, he might as well milk it for all it's worth, and get his name out there early.