Some rules for time travel (for a fictional universe, not based on physics)

First: You can't be in two places at once. More precisely, you can only be in one place at one time. If you are already somewhere somewhen, then you can't go there.
Second: When you leave for another time, you stop traveling through the present. In other words, while you are out in the past or in the future, time marches on.
Third: You have to travel through space to travel through time.
Fourth: How you travel through space is how you travel through time. A trip from time "a" to time "b" requires traveling between two corresponding points in space at a specifc velocity and angular
momentum.
Fifth: Time travel trips move you a relative time distance. So going from the entry point to the exit point at the correct speed with the correct spin will always exit you the same amount of time delta,
unless you are already in that space, in which case you will just continue to travel through the present.
Six: Do you need some sort of special vehicle? Strictly speaking, the proverbial "time machine" is not necessary. Your vehicle merely needs to be precise with respect to coordinate, vector, and spin. In fact, you don't need a vehicle at all,  just precision. Occasionally someone just disappears because they were
walking around a corner at the right speed for that starting and exit place and »BOOP!«
Seven: Occassionally a time traveller tries to visit those intersitial periods between when he left and when he came back. One of three things happens when they come to a time when they already will be there
either they go to the immediate time there after so if they enter at 1PM CST and will already be at 2PM CST for 38 minutes, they may jump ahead 38 minutes after an hour. OR they may snap back to their entry
time. OR they may end up in at a time relative to the entry time plus the length of time spent in another time. Its not clear what determines what will happen.

Some more notes:

"vergere tempus" is the latin phrase for time travel under these rules. It captures the bending, inclined nature of diverge or converge or just being on the verge of something just around the corner. Neither "jump" nor "go" really cut it for me. I want time travellers to adverge from their current trajectory in present time and exverge in another time, only to transverge over a time where they already are, but when they exverge again, they find that the obvergent time from where they already is skipped.

I have a whole love triangle plot worked out based on this.