Time is complicated, and we're not all as cool as Teferi. When a judge call takes place near the end of a round, time extensions can be a little confusing sometimes. This is a quick guide on how to make sure the players are getting the right amount of time.
Here are the basics:
Any time you’re issuing an extension near the end of the round, an easy double check that is that they’ll have had 50 minutes in total. There is no situation where a match should ever have had a different amount of play time.
* This is in case another judge ends up watching the match and doesn't know when the extension is starting from. In the first example I used, where a judge call started at 4 minutes remaining and ended 6 minutes later, the players should get 4 minutes from when the call ends. However without that context another judge would assume that "+4" on the slip means "when the round clock reads -4", which would give the players only 2 more minutes of play time. If you're staying at the match and tracking the time yourself then this isn't as important; you could choose to write +4 or even nothing at all. However be aware that even in this case there's still the chance that another judge walks by and glances at the slip in order to relay that information elsewhere.
I personally recommend always writing the time extension in a way that won't cause a misinterpretation if someone else reads it without talking to you about it. If you think the players might be confused about why they're only getting 4 extra minutes when the slip says "+6", just explain to them that the "6" is referring to the round clock, not their time. (If you don't like the idea of writing "+6" when it's only 4 additional minutes, you could also write "ends at -6" or something similarly more explicit.)
Now for a few examples:
You’re called over to a match when the clock reads 4 minutes remaining. The call takes 6 minutes. What do you write on the slip?
+6 minutes, along with your initials like on every extension.
You’re called over to a match when the clock reads 2 minutes remaining. The match has a prior extension of 3 minutes. The call finishes when the clock reads -2. What do you write on the slip?
+7 minutes. (And remember to cross out the old extension.)
You’re called over to a match when the clock reads -1 minutes remaining. The match had a prior extension of 4 minutes. The call takes 3 minutes. What do you write on the slip?
You’re called over to a match when the clock reads 1 minute remaining. The call finishes when the clock reads -3, and a slow play warning was issued. What do you write on the slip?
+4 minutes, +2 turns