1. If using that date to filter/order a set is not needed.
A simple small date in the relations panel like this:
2. If using that date to filter/order a set is needed (for example to filter/order sets).
Here things get a bit more complex but not impossible in my opinion, this is my idea (even thought this is more like a new feature request): We could have a new “derivate/tracker/connected” relation type that can be set to monitor to another relation and store information about the last time that relation changed.
I’m looking forward to your (and everyone’s) opinion on all this.
A simple and flexible system would just give us an option to choose which relation to track for completion or even let us create multiple relations. So, this could just be a relation type, or this could even be implemented using formulas.
Pipe dream: allow enabling full history, recording every event (in case of multiple checks/unchecks).
Pipe dream plus: have every Object (and Relation) contain meta-Relations that record such events. Most users wouldn’t need to see/use this (this could be disabled by default). But could be very useful for certain situations.