[whpalmer4]

You could create a waiting context, but how will you know when to move the task out of the waiting state?

For tasks which you don't wish to see until some (known) future date, the usual practice is to use the start date field. Set the start date to the first date where you wish to see the task, and the task will be hidden from you whenever you view Available actions.

If the date isn't known, make an estimate. Update it as you get a better idea. You could even make yourself a separate repeating event that reminds you to check if the gating event has happened, and to update the start date.

Another approach is to use the Review feature, and set the review interval for the projects that are waiting on the event so that they are reviewed at an appropriate interval. When you do the review of the projects, you adjust those actions if the gating event has happened.