Royal oak extra thin timing

[Ku5165]

Hi folks!

Finally got an extra thin (5402). Was searching for a 15202 for a decent amount of time and couldn't find any. A 5402 came up as a good deal and I jumped at the opportunity.

Question for all of you, on watches with a seconds hand I track timing using an app. Any recommendation on how to do the same/similar without a seconds hands? A loupe and looking exactly when it lines up with an hour marker?

Thanks!