Trouble with an IF statement

Hi,

I'm having trouble with the following.

I want to do a formula that says,

if cell k68 is equal to or less than 09:00, then write "0", otherwise, 09:00-time in cell k68

I did the following formula but it didn't work. either because of incorrect syntax or possibly formatting issues

=if(K68<=09:00,"0",09:00-k68)