Unfortunately not. We looked into a patch for phpbb, but it strictly works exclusively on a per forum basis rather than being group/permission-based, so in order for normal users to have a time limited edit button of sorts, donators would have to be limited to that as well.
If somebody is willing to code a phpbb solution that adds a time limited edit button based on both user group AND forum, this could very well be done, but as we lack dedicated coders for this (the few active coders are currently involved in the main site rewrite I believe), we can't do it ourselves.
Still, if editing a certain post is absolutely a necessity, you can always request it to be edited by leaving a post about it in the mod drop box or by contacting a mod through some other mean (such as pm or chat), and it should get done in a timely fashion (a few hours wait tops, I would hope). Or you could donate since the org is that awesome.
You can also feel free to double post corrections/addendums, and if I come across the posts, I'll be sure to merge them (I believe other mods do this too). Just try to not do that too much.