Script to automatically trigger by time differential

[merkaba22]

In tasks there is a "begin_task" field created by insert current time.

There is also a "end_task" field created by insert current time.

I have a script to trigger a custom dialog when "end_task" is empty and 4 hours have past the time value of the "begin_task" field.

I can get the script to work manually -- is there a way for it to occur automatically? And for it to occur for all records in the file?