Just like with any repair, how long it actually takes depends on the complexity of the repair, and how much work they currently have in front of them.
I've seen folks on this forum report getting their gun back in 2 weeks after being told 6 weeks, and I've seen some folks say they got it back in 8 weeks after being told the same 6 weeks.
I definitely prefer them going ahead and erring on the side of caution and telling me 6 weeks, as opposed to the practices of some repair businesses.
Ever gotten an estimate from an auto or home repair business?
Every single time I've ever had my car or house worked on, it ALWAYS took longer than the estimate... sometimes 4 or 5 times as long. Now that's infuriating.