To be honest this is a failure from the umpire. It's an international game and you cannot expect all players to understand idioms like "on your own time" easily. In cases like this, as an umpire you have to be as clear as possible. In this case, he should've said "if you take longer than X it will cost you a point, longer than Y costs you a game". It's poor communication to leave it up to interpretation.
This. Lopez looked the ump right in the eye and asked 'What does this mean?! I dunno what this means?!' And he got no answer except for a repeat of. So, of course, he became upset. The ump could have simply said 'there is a 3 minute rest period' or some such, because some ATP codes state this for sets etc. Having said it, I can't find anything hard-coded regarding time for bathroom breaks. Only a '
reasonable time' is quoted in ATP rules, with an allowance of 1 break for 3 sets and 2 for five.
Here's the thing, tho, unlike about all other sports that last longer than 90 mins, tennis has no real breaks. There is no 15 min quarter or semester or period. It is a fairly rushed game. I'm not a big fan of it, and I am sort of looking forwards to Djoker retiring so the shot clock can go back to a warning for the first violation, at the discretion of the ump once again. But because of this, I think allowing a fairly generous and 'reasonable' bathroom break is only fair. Ivashka was savaged by that ump. And let's not forget the other player got the same rest, too. There's no advantage there unless they had a masseuse and hot shower and cocaine in that bathroom break.