what's the best way to get today at 00:00:00?

I have a function that returns today's date/time at 00:00:00, e.g.,
2025-07-24T00:00:00, returned as seconds:

proc start_of_day {} {
    clock scan "[clock format now -format %Y]-[clock format now \
            -format %m]-[clock format now -format %d]" -format "%Y-%m-%d"
}

Is there a better way?