Redis Ordered Set of objects with O(1) retrieval by a GUID key and sorted by another 64-bit signed integer key in descending order

Question

I have a map of sets of unique objects, unique based on it's GUID as key, and sorted by timestamp, a 64-bit signed integer in descending order. The sets are keyed by a GUID and every individual object in the each set should be able to be retrieved by it's GUID in O(1). I need to store this map into Redis cache. I have read of Redis Ordered Set. However, my question is how to ZADD the object into the ordered set for later retrieval by the object's GUID as key in O(1) time and sorted by the 64-bit signed int timestamp in descending order? Thanks.