It would seem that the best time to post on Reddit is around 8-11 (UTC-5). So, if you really want to optimize your timing, try posting around that time. This is when the redditors are online worldwide, meaning more people online to dish out the upvotes.
When one of your comments or posts is 'up-voted' karma is applied to your account. Equally, when your comments or posts are 'down-voted', you lose karma. ... If... more