Koha 3's circulation loans are currently measured only in units of
days. However, because some libraries perform loans that are measured
in minutes or hours, particularly for course reserves and short loans,
LibLime proposes to add support for measuring loan periods in time
intervals shorter than a day. This support will be a new feature,
although it may draw on work that Near Eastern University has done for
Koha 2.

The main changes will include:

* adding columns to issuingrules to specify whether the loan time,
grace period, and charging (fining) interval are measure in units of
days, hours, or minutes

Grah, that's kinda hacky, but I can't think of anything better (MySQL's TIME type only runs to about 34 days; could be a problem).

* adding the ability to define a policy for an overnight loan,
i.e., a loan that is due the following day at a defined time.
* adding display of due times
* adding the ability to calculate overdue fines on an hourly basis

Sounds good enough. Would it be possible to just make due_date a DATETIME type, and set normal day-based due dates to, say the closing time on that day?

This RFC refers to several other RFCs that have been sent or will be
sent soon, including

* System groups
* Opening hours
* Recalls

For more information on this proposal, please consult the Koha wiki at

http://wiki.koha.org/doku.php?id=en:development:rfcs3.2:rfc32_hourly_circ