Is there an easy way to do this? By fully between, I mean don't count the 7am or 7pm datetimes that are equal to the start or end time. 

I imagine this can be done using the unix timestamp in seconds and a bit of algebra, but I can't figure it out.

I'm happy to use something in PLSQL or plain SQL.

Examples:

```
start             end               num_7am_7pm_between_dates
2012-06-16 05:00  2012-06-16 08:00  1  
2012-06-16 16:00  2012-06-16 20:00  1
2012-06-16 05:00  2012-06-16 07:00  0
2012-06-16 07:00  2012-06-16 19:00  0
2012-06-16 08:00  2012-06-16 15:00  0
2012-06-16 05:00  2012-06-16 19:01  2
2012-06-16 05:00  2012-06-18 20:00  6 

```