If someone is waiting on you for a code review, that has to be your P0 task.
Look, waiting on a code review is one of the most frustrating things because the person is literally blocked on you. It gets even worse when there is a time zone difference to deal with.
I get it. You do not have malicious intent and are genuinely busy with something important. But still, I would say it is a prioritization problem. Most people treat code review as something they get to when they have a quiet moment, and that quiet moment rarely comes.
Coming from my personal pain point, I would say treat code review as a high-priority task, not a background one. If your teammate has raised a PR and you are the reviewer, that is important work in progress sitting idle. Every hour it waits is an hour of ‘blocked momentum’ (yeah, fancy term).
Also, it is okay to preempt your non-urgent work for it.
This matters even more across time zones because a delayed review does not cost an hour; it costs an entire working day for the other person (ohhh, this used to be such a pain).
So the next time you see a PR sitting there, wrap up the review, because it is not “someone else’s work”; it is yours.
Hope this helps.