Use minutes instead of hours for download time delta

[sentry-io[bot]]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: backend/donations/views/api.py

Function	Unhandled Issue
post	AttributeError: 'Settings' object has no attribute 'DONATION_LIMIT_YEAR' ... Event Count: 6

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