Is this thing here a helper or a model, or something else?

Manuel Kiessling wrote in post #974606:


for my Rails application I'm going to need a class that does timestamp
computations, e.g. "give me a list of all 5-minute-blocks for a certain
time range".


.set_start_time('2011-01-13 12:00:00')
.set_end_time('2011-01-13 12:15:00')

-> results in

['2011-01-13 12:00:00',
2011-01-13 12:05:00,
2011-01-13 12:10:00,
2011-01-13 12:15:00]

I'm having problems to decide what kind of class this should be in a
Rails application? It really is just a helper and not part of the
business logic, thus it could be a helper, but as far as I understand
helpers are for controllers and views, and this class is going to be
used by models. So, maybe it's a model?

I think it's a model, or simply a utility class that goes in lib.

Thanks in advance,