Thats a great buck! Congrats
The number one thing I believe is getting a quality mount, not turnaround. I'd rather pay twice as much and take twice as long, then get a crappy mount back fast.
Around here, most will typically tell you they try and get everything wrapped up within a year. Of course alot of that is dependent on when you bring them in. If its a bowkill early season, you'll probably get it in 6 mos. Bring it in late in the season...12+mos. The last one we had done (my nephews) took 15mos. They did a nice job, but we didn't get it in until late Dec. Also depends on how many they have to do, and remember...most don't only do deer heads.
It doesn't take long to mount one... its where you are in line that is the wait.
On the flip side, I had a buddy get one done in about 2mos and was cheap. Looked like crap. I told him if it was mine, I'd cut the horns off the mount. LOL