I assume it means that if they call you when you are not at work you have to come in.
But what is "in house call". You come to the job site but only work if needed?
If so can you spend the day just chillin' out unless needed?
Finally, do you interprete a heading like the following 1:3 1:7 1:10
as once every 3 days, 7 days and 10, days respectively?