Yes, based on a local decision (i.e. the local receiver will start to feed data for mlat if it does not see ADS-B positions for a while).
It is fairly common to have aircraft that are on the edge of your receiver range which are ADS-B equipped, but where the low signal strength means that only occasional short Mode S messages (e.g. DF11) are successfully received. The longer DF17 ADS-B messages that carry position information have too many errors to be decoded. In that case you’ll see mlat based on the shorter messages until reception improves.
You may continue to receive mlat results for some time after the local receiver stops sending mlat data (either because the aircraft moved out of range, or because you started hearing ADS-B positions). In that case, as wiedehopf says, locally received ADS-B positions will override any mlat results received.