The default grace period for removal of deprecated reflections is about 4 hours. You should be able to configure it using support key: reflection.deletion.grace_seconds
You can track reflections and materializations using system tables: sys.reflections and sys.materializations
For example:
select * from sys.reflections where reflection_id = '5951c9a6-cbbf-41d7-aa33-95615163c110'
select * from sys.materializations where materialization_id = 'f0c27f88-3d3b-453b-9e97-772965a7e4b5'