Er... By nature if an event occurs every X ms it's timesynced to begin with. The problem with unlimited FPS is some computers might run the game at 100fps, some at 20fps, so on and so forth. You never know. So moving something by 50 pixels every step will vary wildly depending on how fast the game is rendering.
If you're doing things in steps of time anyway, you don't need to worry about it.
Maybe you could elaborate exactly what you're talking about, because what you've listed is the same as doing 100ms x 50, x 100, x 150 (5 seconds, 10 seconds, 15 seconds).
Why don't you just "do this every x ms" (every 5, 10, 15 seconds) ? Why bother adding to a counter?
EDIT: Missed this question:
[quote:10frcve3]Also, unless I misunderstood, Time Delta varies. This means the value will never actually be exactly 50,100, or 150, right?[/quote:10frcve3]
Sure it varies a little (or can a lot), but it ultimately depends on how much you're doing each step. If you load resources at random times during the game it'll sky rocket when you do, compared to if it's humming along just doing the same stuff every frame.
TimeDelta is usually a very small number. For example 0.0013. It's the time it takes your computer to perform 1 game loop. Even on a "slow" computer, it's usually a very small number (compared to whole numbers). Most computers can render a basic game at 60fps solidly with vsync on. Mine can run my sample projects upwards of 10,000 at times with it off. That's a really small number
I can't think of a reason you'd need to be using TimeDelta in a cumulative fashion like I think you're attempting (even though it's not in your sample you give). Construct does this for you by offering the "every X ms" event.
But again, unless you elaborate more, I can't even fathom what it is you are trying to accomplish. But to answer your question... if you are adding it cumulatively every gamestep... if you're casting it into an integer, it will eventually land on the whole number you're after. Yes. But if you happen to do something time consuming at that moment, it may skip over the number you are after. I'd encourage you to use greater than/equal to as opposed to just equal to.
But for more accurate time calculations, just use what construct offers.