There are two spawns on earth that you can pretty much set your watch to, and thats the Mothyards (Warsat/enemy/crew) X:00 and X:30 and the Divide (walker) X:10-15 X:40-45.
There are four other spawns that are hit or miss, the Steppes (Warsat/enemy/crew) X:15-:25 and X:45-55 forgotten coast (Warsat/enemy/crew) X:35-40 and Skywatch (Warsat/enemy/crew) X:00-:05
X:00 Mothyards: I start my loop at the Mothyards a couple minutes before :00 sometimes this one comes a minute or two early or a minute or two late but it always shows up. if you kill this one early enough you can make it to the skywatch for the X:00-05 event if not then you can move on to the divide for the walker
X:10 Divide: You want to get to around X:10 or so if you can, the walker unusually doesn't show up until X:15 but sometimes hes early.
X:15-25 Steppes: Here you want to hang around the steppes, sometimes an event will show up sometimes it wont, its really hit or miss if no event shows up by X:27 head over to the mothyards.
X:30 Mothyards: As before this one is sometimes a a minute or two late/early but it always shows up. when are done with this you to need to head to the forgotten coast as quickly as you can.
X:36 Forgotten coast: this one usually spawns right at :X36 its been late once or twice but if its not out before X:39 its not coming and you need to hurry on to the divide either by orbiting and coming back or really fast on sparrow.
X:40-45 Divide: This is the walker again its pretty simple after you are done head to the Steppes like before as quickly as you can
X:45-55 Steppes: This is the last one, ive seen this one only a couple of times it rarely spawns, but i have seen it.