"Having a manual number input with a [(seconds /) minutes / hours / days] selection next to it would be the most granular approach even if it wouldn't look that good. Or 3 sliders, from 0 to 59 for minutes, 0 to 23 for hours, and 0 to 7 days. That would allow sharing for an hour and a half instead of having to put 90 minutes with the number input. Reset the previous sliders to 0 if you set the expiry to 7 days, which would also be the default expiry time like it is now.

Having a more granular display could be behind the "Show advanced features" option we talked about, so that wouldn't clutter the interface for all users by default, but remain there if people want it."