When do Church bells ring?

I am finding some ambiguous information about this. Would anyone have any definitive information?

The reason I am asking is that I have been assigned to design the entrance to an abandoned Covenant.
My idea is the Covenant (stolen from something I vaguely recall reading somewhere) was in a cavern in a Magical Regionne. The entrance to the Regionne is in a Magical Aura. However I am saying a sanctified church was built on top of the Magical Aura, suppressing it with the church's Divine Aura.
Except on Midwinter Day. Between sunrise and the first tolling of the church's bells, the Magic Aura re-asserts itself, and the Magic Regionne is accessible.
My question comes down to - what is the typical time before the bells ring on Mid-winter's day?

BTW Does the above idea sound familiar? Anybody know where I got it from?

It will depend on the location. In some places church bells ring the hour- as in modern timekeeping hour. In others they ring the liturgical hour. Matins ends at dawn, so if the church rings the bell at the end of service your folks are out of luck, the window would be measured in seconds. If the bell is rung only as a call to service then they will have between dawn and first hour- which is sometime between dawn and "9:00", in a system where 9:00 is defined as being halfway between dawn and noon, so roughly 1/4 of the daylight hours on the shortest day of the year... hopefully this location isn't too far north, in Hiberia, Loch Leglean or Nogorod this won't be much time...

What is the function of the church? Who is in charge of it? Is there a priest and helpers always present? Where is your saga placed?

If a church has bells and services a 13th century Western monastery, you can expect the bells to ring for the Prime (about 6 am) first.

If the church services a 13th century catholic parish, its bells are more important: they have to call the parishioners for mass from further away, and might from the later 13th century on toll for the Angelus prayer around 6 am, noon and 6 p.m.

To sum it up: for catholic areas around 1220 you can make about any decision for your campaign.
On one hand, there might not be any bells in a small monastery or hermitage, or a parish church might not always have people to ring its bells and only tolls for service.
On the other hand, a rich monastery or fervently pious parish priest might have the Angelus tolled daily on a big bell already many years before that became customary.

Cheers

Thanks One Shot and silveroak.
It looks like this is a workable idea, and I can pass it onto the SG to customise as he needs it.

I think the ambiguity I had looking for the answer stemmed from the fact that my modern mind was convinced that an hour was an invariant length of time.

Hour as a measure of time! Its actual duration depends of the kind of wood you have at hand, its humidity and how big your grogs' biceps are: Grogs give a wonderful definition of an hour as roughly the time it takes for a log the diameter of a man’s arm to burn.

It also says that people measured time mostly by the sun's height during the day and moon/starts height at night, so in the medieval setting our day "hours" would be longer during summer and shorter during winter. So probably instead of bells ringing at exactly 6 AM, maybe after sunrise in summer and still at night in winter, you'll get bell ringing at dawn every day of the year. So if you heard bells and it's not the middle of the day or night, renew your Parma.

In fact measurement of time, shorter than days, was something that became progressively more obsessive during the middle ages, starting from position of the sun and water/candle clocks up until the early renaissance where metronomic clockwork was established in order to determine the proper time for prayers. How quickly this progression occurred will vary by location as well. It would seem the first use of falling weights instead of water based clocks in Europe was probably around 1280, and pendulum based clocks which were the first that could be considered reasonably accurate by modern standards was invented in 1656. Most timepieces in 1220 would be calibrated frequently to match the sundial.