My cat is kept strictly indoors... my reasoning is that we live in the country and I have over $300 invested in vet bills on him! We have lots of strays in the area, and our neighbor has a few outdoor cats, and there are a lot of dogs that wander around, not to mention skunks, opossums and coyotes too. I fear for my cat's life!
I can tell you that my cat sleeps pretty much when I do. We go to bed around 12am every night, and if I stay up later he starts following me around and swatting at my legs and meowing constantly until we go to bed. Then we take a nap every afternoon (because I'm pregnant) and he's usually ready for that between 1pm and 2pm. If I don't go to bed when he's ready to go he meows a lot and runs back and forth between the stairs and wherever I'm at.
He usually hunts for an hour or two in the late evening, around 6 maybe. We have a rather elusive mouse that he really wants to catch but it never comes out in the open. But still, I see him sitting right in front of the wall where we can hear the mouse, and he sits there for awhile every day.
Play time is most of the rest of the day. There are several scattered cat naps but he's only 6 months old so he still plays a lot. He attacks my dog, my mom's dog, house plants, his cat tree, his springy toy box, and any other item within his reach. He's most active in the morning when I wake up though. For the first 2 hours he's pretty wild, running full speed through the house and whining. He talks a lot!
I had another cat who was mostly an outdoor cat, but she no longer lives with me. It was hard to track her daily activities because she'd disappear for two or three days at a time, but it was on a regular basis. She came back with something dead every time too, things like bunnies, squirrels, lizards, turtles, birds, snakes, she got a crayfish once, a mole, various rats, mice, basically anything she could grab and carry. Truly a hunter, so I have no doubt she was constantly hunting the whole time she was away. She didn't have any other cat friends. She actually hated all other cats except for one that was her brother. I had him until he was like 4, and she was 5, but I had to rehome him when I moved because at the time I couldn't have any pets. She's now 9, and she lives with a friend in Missouri... she's living a spoiled tree hippie kind of life lol. She was seen (on several different occasions) attacking the neighbor cats here and chasing them off our property. That's why she lives with my friend, no other cats there. She seems happier that way.
A cat in your back yard or garden can be explained by a number of things. Some cats have a several square mile territory that they roam, while other cats prefer to keep themselves in a smaller space. Even females mark their territory. Your cat may have overlapped scent markings with this particular cat you speak of, try keeping an eye on them and see if they're friendly together. They may have made friends, or enemies. It's hard to say. Some cats just wander into other cat's territories for no reason other than wandering.