When to use "around" and "about"?
When used to indicate an approximate time (your first example), "around" is more common.
When used to indicate an approximate duration, either will do, but "about" is probably more common. No particular difference in register, though.
I'm guessing that your first example should be "I'll arrive around 3 pm" while your second should be "I've been here [for] about/around ten minutes".
(British usage)