I think it's important to point out the difference between:

1) the time limit you've got to 're-edit' a post without the forum adding: "edited by John Doe (date/time)"
2) the time limit you've got to 're-edit' a post with the following added: "edited by John Doe (date/time)"

I believe Nigel currently has it set up to allow people to edit their post up to 10 minutes after it's initially posted.
In addition to the opportunity to take 'as long as you need' to PREVIEW what you write BEFORE you hit send, the extra 10 minute grace period gives the poster another generous opportunity to amend/change their post for spelling/syntax or to take back what they originally said . After that point, the post remains permanent. This seems 'more than' fair to me.

That said, if and only if the forum software supports it, I too would appreciate having a short 5 minute grace period after the initial post where the poster can change/edit their post without it appearing as: "re-edited" , but then: only 'another 5 minutes more' allowed to re-edit, but now with the "edited by John Doe (date/time)" added. After 10 minutes total time, I feel a post must remain permanent, and only be changed or removed by contacting Nigel.

I believe the current 'ten minute limit' will greatly reduce the past problems where certain members were too conveniently able to erase, change, or alter the meaning of their initial post later, simply to protect them from recrimination, or to suit an ever changing whim: often minutes and sometimes hours later.