Change TimeValue to reference a Cell entered value instead

EditDate = Now
    Application.OnTime Now + TimeValue(Sheets("main").Range("A7").Value), "TestForUpdates"

I cannot seem to get the correct method for the above to work, instead of hard coding the set time in hh:mm:ss.

Am i missing something obvious ?

What do i set the cell format to hh:mm:ss or number etc ?