There is no way to define such a type. There is a proposal on GitHub to support this, but it currently does not appear to be a priority. Vote on it and maybe the team might include it in a future release.
Edit
Starting in 4.1 you can define a type that would validate the string without actually defining all the options:
type MarkerTime =`${number| ''}${number}:${number}${number}`
let a: MarkerTime = "0-00" // error
let b: MarkerTime = "0:00" // ok
let c: MarkerTime = "09:00" // ok
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