First of all: English plz! There are alot of german people in here but like 99% does read english, whileas the english people mostly do not read german .
I hope I interpreted 'straightforward' the right way in the following explanations/theories, else my blabla is kinda pointless .

IMO time is the dimension before 1D, 2D and 3D. There are theories that you can go back or forward in time but does that mean that time is not straightforward? Or is there something else they found out that time cannot be straightforward? If being able to go back and forth in time means time is not straight, I put a questionmark for this statement.

I don't know too much about time, but I thought that you could only go forth in time, and not back, that is, not back in time and be on the same place. If you go back, your position would be at a point as far away as you went back in time. So it would take time to go back and when going with the speed of light you'd end up at the same time as you left there. So, in this theory, going back does not mean that time is not straightforward.

Does going forth imply that time is not straightforward? If you go forward in time, it could, and this is just a wild speculation of me, be the case that not only time is bended, but all dimensions are bended at that place. (seems logical to me: when you shrink a 1D line, you'd make a rectangle out of the square, and if you shrink the square, you'd deform the cube, so why not deforming the dimensions when deforming time?). Goes for vice versa as well, and this probably is the case too. When you shrink the cube, you shrink the square, the line and time as well. If we have a lot of gravity at one place, so much that even light can not escape (a black hole), maybe the cube is deformed by the gravity and causing a deformation in the timeline as well. But this doesn't mean time is not straightforward. When everything is bended there, time would relative be straight again, eventhough it looks like bended from the outside. (Like the person who falls into the black hole falls with a constantly increasing speed, whileas the person who looks at it sees the person falling with a decreasing speed).

So maybe this was one big bullpoo talk, and maybe I said something usefull . But this is how I see time atm. (Though I didn't involve movement-slows-down-time)