Image courtesy of digitalart / FreeDigitalPhotos.net
If you do reach a limit, we'll let you know with an error message telling you which limit you've hit. For limits that are time-based (like the direct messages, Tweets, changes to account email, and API request limits), you'll be able to try again after the time limit has elapsed.
The Tweet limit of 1,000 updates per day is further broken down into semi-hourly intervals. If you hit your account update/Tweet limit, please try again in a few hours after the limit period has elapsed.