what is the least time a company has to pay for compassionate leave?

Answer 1

Zero Days.

Companies are not required to pay any compassionate leave!

Those that do offer it, cannot offer different amounts arbitrarily, but must have a written schedule, or contracts with individuals stating what is offered.

Answer 2

A company does not have to grant compassionate leave at all if it doesn't want to. In UK compassionate leave is only contractual.....ie. it can form part of your contract of employment. There is no right by law to it.