Your suggestion for users to be aware of multiple time zones is valuable. Users should, however, be careful when retweeting their own content to capture all markets. I think the most honest approach is to own up to what you're doing. RT-ing with an explanation, such as 'RT for the US: 'original tweet' ' Or similar. Just a plain old 'RT @myself 'original tweet' ' comes across as amateurish and could be interpreted as over pushy – certainly if it's done multiple times.