Since you are going to let them walk in, I would definitely do it right now. I bet they will move in real quick. One caution, they will not be happy bees especially in the rain. At my daughters christening party, 30 years ago, one of my dads hives swarmed and landed in a small tree right front of the of their front door just as the party started. He just shook his head pulled out a hose and sprinkled water over them to get them to ball up real quick and then he shook them into a trash can. My father in law was there and asked about getting the bees. My dad told him over and over again that they would be a hot hive but he took them any way as his first hive. 5 years later, while visiting, my dad was able to tell which hive it was, out of 20 hives, because they were still hot. One note, they were always his biggest producers.