>>> def time_diff(t1: str, t2: str) -> str:
...     def to_seconds(t: str) -> int:
...         minutes, seconds = map(int, t.split(':'))
...         return minutes * 60 + seconds
...     diff_seconds = abs(to_seconds(t1) - to_seconds(t2))
...     minutes = diff_seconds // 60
...     seconds = diff_seconds % 60
...     return f"{minutes}:{seconds:02d}"
...
>>> time_diff("9:56", "18:37")
'8:41'