How quickly should oil pressure come up?

One of the great "features" of a Mopar engine-

They will "tell you" via the lifters when you are low on oil (add oil and clatter goes away) or need to change the oil (add oil or dipstick shows full, but clatter doesn't go away).

10/40 shouldn't be a problem. I've run 20/50 without issue.

...but it sounds like your oil might be breaking down. How old is it by calendar age and by miles?

BTW- I don't subscribe to 3K mile oil changes. I've done 5K since the 1980's.