ReportViewer Formula

Guys using the below formula, the Fields!Monitor_Time.value is an int, how can I tell the formula to convert to the for mentioned string and deduct from the other Value, my attempt is below 

=System.String.Format(

"{0:00}:{1:00}", DateDiff("n", Fields!Docket_DateRaised.Value, Fields!Docket_EngFinish.Value) \ 60, DateDiff("n", Fields!Docket_DateRaised.Value, Fields!Docket_EngFinish.Value) - (fields!Monitor_Time.Value) Mod 60)