If you look in the Resources section under Rules in the right side bar you'll see Q proofs that point to such things as deltas. KillerBunny88's link to the Ultimate Q Proofs video is also very good regarding explaining deltas.

I also stumbled upon a delta myself, though not in the "exactly x years from now" type but a more complex type called a Q Clock delta. There's a device called a "Q Clock" which is basically a spiral calendar with a 60-day revolution. The post in question was Q post #16, posted on Oct 31, 2017, which told us to get our popcorn ready for a Friday and a Saturday and states that POTUS is "insulated" from impeachment. Exactly 1200 days later (20 x 60 day delta) on Friday Feb 20, 2021, we saw Trump's team absolutely shred the impeachment arguments and present montage after montage. The very next day on Saturday Feb 21, 2021, Trump was acquitted and the Left was left utterly salty.

https://greatawakening.win/p/12hRQKrIt5/q-clock-q-post-16-and-trumps-acq/c/

Note that deltas are difficult to find and calculate unless you're really familiar with dates and times, have read the Q posts almost religiously, and eliminated possible false leads.