There are ratings, and limitations.
The ratings are for the power produced, and the limitations are for protecting the engine to allow continued use.
Some engines have cumulative limits on OEI use - the P&W 206/207 engines that use 30" ratings, for example, have a cumulative life of 2 minutes at 30" power, and then the engine comes out for maintenance.
The same engine can be used in different airframes with different ratings - some airframes use 2 minute and 30" ratings, which have very tight tolerances on exceeding the limitations in those ranges, while another airframe may use 30 minute and 2.5 minute ratings which have more generous exceedence limits.
Confused yet?