If it continues into tomorrow or the day after, then unfortunately you have to consider it a sign of returning fertility instead of just lochia. 56 days is the cut off, but one extra day isn't a big deal. If you're still bleeding a few days past that, can't take chances and assume it's lochia.

The heaviness doesn't determine whether it rules out LAM or not though, the timing does. Some women have a very heavy bleed before 56 days is up and are still in LAM, but this seems to be cutting it a little too close.