A reasonable time ok BUT RANDOM.... else the bots will vote exactly after 1, 5 minutes or 10.... they will not care if a minority of users voted before them....
And I don't agree 1 and 5 minutes is reasonable in a 24 hour period... I find more reasonable 1-2 hours before the original voting power kicks-in. We want average users to have the opportunity to get better rewarded ... And average users are not logged in 24 hours a day to take advantage of 1 and 5 minutes windows... I mean average users will have a bigger selection and will vote with less pressure if they have more time to read the content before voting....
Look what happens now, we upvote most of posts because we read a nice title (because we are in hurry off course) and then we read the underlying content :)