If your internet is rural like mine, 3.5Mb/s then it'll take a good few hours!
Have you got at least a 3Gb microSD card in the Zumo? I've got an 8Gb one in mine - as that's all Asda had on the day I went... They didn't have any 4's.
You must have a card in nowadays to cope with the size of the map download. Using Garmin Express is so much easier than the old way.
If you're plotting routes abroad, once it's worked out on the Mac, remember to click the send maps box when prompted, not just the waypoints etc.
Now you have plenty storage, think about clicking on a few extra map tiles if you are going to wander off the A-B, B-C, C-A routes as it'll only bring over the ones definitely needed for the routes you're sending.
Hope that makes sense. If not, PM me.