Difference Between Two Times - Is it 30 minutes or more?

[Ark68]

I have two times, curr_st and prev_et.
I need to figure out how many minutes there are between the two times.
If there is 30 minutes or more between the two times then do one thing (set svc_off = curr_tt - 30 minutes), otherwise, do another thing (set svc_off - curr_st)

This is my code:

tdiff = curr_st - prev_et 'time difference
If tdiff < 0.5 Then
     svc_off = curr_st
Else
     svc_off = curr_st - TimeSerial(0, 30, 0)
End If

When curr_st = 45117.75 (6:00pm), and prev_et = 45117.6145833 (2:45pm), there is clearly 30 minutes plus between the two times.
But my code triggers the "If tdiff < 0.5 then" statement, which is wrong.

I think the "If tdiff < 0.5 then" is wrong.

How do I correct this?

 

[PeteWright]

You need to keep in mind that 0.5 does not equal 0.5h (half an hour) but 0.5d (half a day) since 1 equals one whole day (24h)
Hence 30 minutes would be calculated as follows:

1h = 1/24d
0.5h = 1/48d = 0.02...

tdiff = curr_st - prev_et 'time difference
If tdiff < 0.02 Then
     'less then 30 minutes
Else
     '30 minutes or more
End If

 

[MARK858]

Another option...

Sub mindiff()
Dim tdiff As integer, prev_et As Date
Dim curr_st As Date, svc_off As Date

prev_et = TimeValue("6:45")
curr_st = TimeValue("7:30")

tdiff = DateDiff("n", prev_et, curr_st) 'n is minutes

If tdiff < 30 Then
     svc_off = curr_st
Else
     svc_off = curr_st - TimeSerial(0, 30, 0)
End If
End Sub

 

[Ark68]

Thank you both for your solutions. Both worked. Solution credit to you as well Mark.