Let’s say you email me and a ticket is created. I email you back in 5 minutes and resolve the ticket. You write back a day later and I resolve the ticket in 5 minutes again. Currently, the time-to-close metrics on Hubspot would return this as closed in 1 day 10 minutes. It only takes the date/time opened and finds the difference with the date/time of final closure. It does not take into account that the ticket was closed for 1 day and only actually open for 10 minutes.
A better time-to-close metric would count only the time a ticket is actually open.