Allow routes to reference time intervals
Allow routes to reference time intervals

Signed-off-by: Ben Ridley <355023fe1c8f86a7ebed12a304e34c56a0753505@gmail.com>

GoogleCloudPlatform/alertmanager,prometheus/alertmanager,prometheus/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager,prometheus/alertmanager