Max takeoff thrust is usually time limited to 5 or 10 minutes.
From Boeing:
Takeoff thrust may be used only for a maximum of five minutes, with one exception: the time limit is extended to ten minutes for airlines that have purchased a special Airplane Flight Manual appendix called the “ten-minute appendix”.
The Certificate Limitations section of that appendix states specifically:
“The time limit on the use of takeoff thrust is increased to 10 minutes provided this use is limited to situations where an engine failure actually occurs and there is an obstacle in the takeoff flight path.”
Last edited by underfire; 6th Oct 2017 at 17:10.