check column for value and show message box

Hi all,

I know this will be a if then macro but I don't know how to write these. Basically what I am looking for is a macro that will check column J from A2 down for a value of 75 or larger, if over or equal to 75 show message box ( i'll figure out what to say in it later), if the numbers are all under 75 show message box "done". the numbers are times in mm:ss.

Thanks in advance.