Yeah I would try to resettle after 40 minutes, or get them up for an hour or something, and try them again. DD2 was doing this, and now has dropped to 2 sleeps a day, but each sleep is a good hour or so, which I'm happy with. She does turn into a little grizzle bug around 5pm though, so I put her on my back in a sling so I can still cook dinner and do stuff with the other two.