Metatime

Metatime is a time system that is separate from local time. Any events that take place outside of a timeline work under it.

Meta Note: It's been decided unanimously that time travelling through metatime will never be possible. It is very important that this limit is place in order to allow the roleplay to remain comprehensible.

Mechanics
[This is still a little bit of a wip - please ask for clarification if you need it!]

Timelines fall under their own individual local time systems due to their 4D structure. Local time occurs separately from meta time, continuing on its own. Typically they require another dimensional structure, which 4D serves as for timelines. Any events that either take place with time travellers or outside of 3rd dimension are influenced by metatime.

While these scenarios are not natural, certain reality warpers or technology can create their own local time that takes place separately from metatime. There are also some separate multiverses that have their own internal time systems due to their own structures. Although timelines are definitely the most notable example of places that have local time, they aren't the only ones that have them. It is difficult but not impossible to put entities from higher dimensions under local time with the right tools, though such tools are not common knowledge. However, as many of them have their own navigational abilities (dimension is an umbrella term, not a statement of power), it's not guaranteed to work on everything.

Some Practical Examples
Let's say for example you time travelled to the year 100BCE, then 3000 CE, and then back to your own time of 2021 CE. To another traveller that is observing you, in what order did you travel in? We refer to the perspective of metatime, which because you are a time traveller applies to you. It applies to the other traveller as well, which would have seen you travel to your past, then future, then back to the present in that very order. They would also observe the amount of time it took you, due to currently interacting with something outside of the timeline.

Here's another scenario. Your time machine broke in 3000 CE, disconnecting you from any contact outside of your timeline in the process. You have to spend a year finding the materials you need to fix it. What does it seem like from the perspective of that time traveller now? Because you became a part of the timeline for that time period, the observer wouldn't even be able to tell any time passed between your timeline breaking and you fixing it. This is because timeline time runs separately from metatime.

It should be noted that local time can sometimes delay from being instantaneous, but this tends to happen for time periods beyond just a year.