Try using Install OnTimer Script to perform a script 300 seconds (5 minutes) after the script with the Install OnTimer script is run.
If you use the OnTimer, keep in mind that every new window you open with that window active will start a new timer.
So, when using OnTimer it is useful to insert the OnTimer step as empty at the beginning of the new window script step to prevent this.
Filemaker needs a new New Window step that opens a blank window with no triggers, alarms or other hangons. Or maybe just a checkbox in the New Window Dialog:
__duplicate window __blank empty window