I went to get my TB replaced at about 70K, my mechanic (this is why I go to him) told me that for the civics, it should be good to about 95K or so.
I was extremely happy to put off the cost at the time, but once it gets up to around 95K, you can bet its gonna be in for a change. Heard too many horror stories of timing belts breaking and engines getting screwed up.