A short time frame is fine because the consequences for missing it is that rent is delayed until the repair is complete, or the tenant is authorized to arrange for repairs themselves and deduct the costs from the rent. Neither of those are onerous so there doesn't need to be a long grace period.
This is also specifically for safety related repairs. It's not like a tenant can withhold rent for a broken window screen or dripping faucet.
The issue is the ambuguity in what someone intends when they just say radiation. It is valid to call any electromagnetic wave radiation. However, as for health concerns, what matters is "ionizing radiation." Microwaves are too low energy to be ionizing, so they don't match what most people think of when they say radiation with the implication of ionizing.