From an affiliate manager/industry guru viewpoint, I think PRO-actively managed programs
SHOULD approve apps in 48 hours MAX!
However things happen, like vacations and AMs being out sick.
Many programs are under-staffed or don't have an AM at all, so approvals can take a long time.
Then again with very large programs that get TONS of apps, I'm sure some AMs so some cherry picking. Scan and approve the 3-4 bar earners and skip over the 0 bars until they find time when they are caught up with everything else. Hate to say it, but I remember doing that. When you have 14 hours of work and only have 8 hours (in a corp job) to do it all, sometimes you just do the best you can to try to keep up.
I think if I was an affiliate right now if a merchant I REALLY wanted and needed didn't approve me in a 4-7 days I'd email them. If it was a so-so merchant I didn't critically need, I might wait 2 weeks then either contact then or just say forget you and find another merchant.
I'm sure when you are just getting started and need approval to finish the site the hours probably feel like days and the days like weeks. Waiting isn't fun.