One current effort to put some numbers to this question is SciRev (https://scirev.sc/). It allows authors to "review the review process" and document their experiences with journals in a public (but anonymous) way. Based on 41 reviews, it looks like the mean handling time for an accepted paper at PLoS ONE is ~3.5 months (time from submission to acceptance).
There is not much data yet on most ecological journals, but the more we all contribute our experiences (both positive and negative) the better it will be in the future! -Sam Zipper
