While it’s not immediately obvious, you can create a workaround to allow you to use Actual Time as a rule trigger now that number fields are supported as rule triggers.
If you create a second custom field as a Formula field, go to advanced mode, then add Actual Time into the formula, Formula fields are supported as rule triggers.
Additionally, if you add a +0 to the formula (as shown), this will cast the output into a Number type instead of a Duration type, which means you can do arithmetic comparison with other number fields in Asana.
For example, you can then create a second Formula field containing a formula Estimated time + 0, and you can create rules that compare Actual time and Estimated time.
