I’ve never flown cargo but I have many friends who do so let me add a little to Chris’ answer.
As Chris said, UPS and FedEx pilots are some of the highest paid in the industry, making those gigs very tough to get (but again, not impossible). Atlas is probably number 3, they pay well (not great) but they’ve been hiring like crazy for years due to expansion and turnover. UPS actually has a different pay structure than most airlines. They pay strictly based on seniority vs aircraft type. Of course pay increases at all airlines as you gain seniority but also most pay more money for larger aircraft, so you’ll usually find the larger aircraft have the most senior pilots because they want to get paid. While this is all well and good, often pilots are “forced” to fly aircraft (and hence routes since they follow the aircraft) for the money vs what they like. Good example here at Hawaiian Worldwide has always paid more the Interisland but the gap used to be small so Interisland was actually very senior because the quality of life was much better. In the last contract the gap got significant and there was a huge shift in seniority. Anyway it’s kind of cool because at UPS you have pilots flying the equipment and routes they enjoy vs which pay the highest.
Now back to routes and times. Again all flying at all airlines including cargo goes by seniority and no not all flying is at night. It’s a great big World so logistically, if you think about it, it can’t be. The more seniority you gain the better routes and flight times you’ll get.
The biggest complaint I hear from my friends is the duration of the trips (again gets better with seniority). Obviously all carriers strive to be as efficient as possible and that’s more vital when you’re talking long haul. So while most airline flights will fly say from LA to Beijing and then return to LA, due to trade agreements, contracts and other factors cargo is often different. You may find yourself flying agriculture to Korea, then hoping over to China to bring textiles to Japan, then taking electronics from Japan to Asia etc etc. What that means is many cargo ops can (and sometimes) will have you gone for weeks at a time. On the plus side that’s usually followed by weeks off as well. Some pilots love it, some don’t.
Either way, as Chris says, unless you have an in with the CEO you should plan on starting at a Regional flying passengers first. You may find you like it? If not there are plenty of boxes waiting for you.