

Yeah, as in, if you take a quarter of an hour (15 minutes) from 10, it’s 9:45.
They also use minus ten, minus twenty or even minus twenty-five.
Ten hours minus twenty-five is 9:35.
Ten hours minus twenty is 9:40.
Ten hours minus (a/the) quarter is 9:45.
Ten hours minus ten is 9:50.
I find it confusing and never got used to this system. It feels old fashioned and it’s not even faster to say. But it’s still pretty common while being informal.
It works and would be understood but it would also be odd. The unwritten rule is to round up to a multiple of 5.