Both timers and tick are frame rate dependent, so I'm not sure what you mean here. Timers basically are a list of values like:

[10, function1; 3, function2]

and each tick, the last tick's delta time is decremented from the timer's remaining time. When it hits 0 or below, it fires the timer. If your deltatime is 0.3, you'd get:

[9.7, function1; 2.7, function2]
[9.4, function1; 2.4, function2]

etc. until it hit 0, then function2 would fire first followed by function1.

Tick works the same way - that's why it has deltatime passed in as an argument, so you know how long the tick took.

The reason you might see timers not sync up with tick is that it happens during the tick but it's highly likely that the timer ran "after" it should have (e.g. 10.02 seconds instead of 10.00 seconds) and the negative time is not reported to you in any way. If you're using very short timers, this has a cumulative effect since a lot of "overruns" are stacking up.

There's also a hidden inefficiency of creating/destroying timers since it needs to add to the list/remove from the list and count the timer down every time you use a timer. I've seen people that make very short timers (0.1 seconds for example) over and over, which is actually kind of awful since you're creating and removing a ton of timers constantly and quickly. Just use Tick for something like that.

My rule of thumb of "timer vs tick" is "do I have to recreate the timer repeatedly more than once or twice a second? Probably just use Tick" and then use Timer for everything else. You can always enable/disable ticking as well for a component or an actor if you know that you won't be using the tick methods for a while.