Time entry validation fast formulas

Summary:

We need to create a time entry rule to validate that if a project is entered on the timecard, the project task is now required too.

Content (please ensure you mask any confidential information):

We have a template where we have project / task on it, but also a time type column for when we are not working on projects. This means that we cannot put the Time Entry Layout Component as required, therefor we need to validate this using another way.

Can you provide indications which object/inputs I can use to create the fast formulas for this rule ?