We usually observe silence and prayer in the afternoon of Good Friday in our household. We don't put a time limitation on it, but this year we have some people who could benefit from our help coming by and we'd like to help but I'm afraid they'd be intruding on that time of silence.
What is the usual length of this period of quiet in your household?

Traditionally, it's called Tre Ore and it lasts from noon til 3pm.

Thank you!
I googled it and apparently there's a plenary indulgence attached.

I can't find it in the current list of indulgences. There was a general reset of indulgences in 1968 and many were not kept.

I was just googling and saw something about a 2006 manual of indulgences put out by the USCCB... but couldn't immediately find an online (free) source to the whole thing to browse..

Search for enchiridion of indulgences. It's been reissued several times, but I believe the changes are minor.