Welcome to Android Central! Which phone do you have, and what wireless service do you use? Are you unable to connect at all, or only after using a certain amount of data? Do you have unlimited data or not? If not, did you hit your monthly limit? With some services, that might prevent you from connecting--other services might just start charging you for every MB of data you use over your limit.
There isn't really a time limit for usage--it's the data.