fix(venues): resolve mismatched selected time period

[Beebeeoii]

Context

This PR closes https://github.com/nusmodifications/nusmods/issues/3821.

Implementation

For context, this was probably broken because of the added support for 15-min intervals (https://github.com/nusmodifications/nusmods/pull/3771) which caused there to be 4 periods in a single hour. This PR resolves the issue by replacing the hard-coded number of periods in an hour.

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 54.60%. Comparing base (2d4743d) to head (21d5674). Report is 25 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3822 +/- ## ========================================== + Coverage 53.87% 54.60% +0.72% ========================================== Files 274 274 Lines 6032 6053 +21 Branches 1449 1446 -3 ========================================== + Hits 3250 3305 +55 + Misses 2782 2748 -34 ```

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[zwliew]

Thanks!