vb中时间处理的溢出问题

startTime = rs.Fields(3).value
endTime = Time
diffMinute = DateDiff("s", startTime, endTime)
diffMinute = diffMinute \ 60

useHour = diffMinute \ 60 '使用时间 小时
useMinute = diffMinute Mod 60 '使用时间 分钟
If useHour = 0 And useMinute < 5 Then
myPrice = 0
Else
myPrice = useHour * Form5.Text4.Text
If useMinute <= 5 Then
myPrice = myPrice
ElseIf useMinute <= 30 Then
myPrice = myPrice + 1
Else
myPrice = myPrice + 2
End If
End If

这是代码
startTime和endTime时间间隔一长 就提示溢出
定位到diffMinute = DateDiff("s", startTime, endTime)