I always go into lock down a day early, yes. For the seramas, I'm going two days early. It happened that I got some "surprise" eggs in a batch that probably were Seramas. (They are awfully small.) I had a lovely day 18 hatch. Luckily I had moved them a day early with some others so the little ones had a chance to turn while not in an auto turner. During the hatches leading up to the Halloween hatch, I had a couple happen early anyway due to temperature spikes and drops along the way, so I still think it's a good idea no matter what you have, if you have doubts about your incubator. That said, I've also hatched on days 21-23 before, so not just early.
This time I have a mix of ducks, silkies, and seramas. (The ducks are staggered to hatch about the same time as the silkies and seramas.) Everyone will go into lockdown on day 16 for the seramas. I don't think it does any harm and it may do some good. I just can't believe it's almost time. lol It seems like just 3 weeks ago I set that Laundry Room egg... (He's hatching today, in the other thread.)