help expression

[qliklizzy]

Hi

Could someone help with this - it works - but i need it to calculate the percentage of MinAnaesthetistStart times that started within 10 minutes of the MinSessionStart but include all those that started before the MinSessionStart? 

sum({<OperationOrder={1},MinAnaesthetistStart ={"<>''"}>}  {<CancelledOnDay={0}>}

     if( frac(MinAnaesthetistStart) <  (frac(MinSessionStart) + interval#('0:10','h:mm')),1,0))/

count(DISTINCT{<SessionUsed={1}>}  SessionID)