I find the timing rather curious as well. Based on what has been reported so far, SB and TM's normal Monday would have been mom going to work and TM going to day care, now that school is out. Neither showed up at either place, but witnesses see Stocky Black Man and Girl Matching TM's Description getting OUT of SB's car (parked several blocks away??) and into the gray sedan, at around 11:30 in the morning. So whoever this guy is, was either in Sara's house overnight or very early that morning.
CPS tracks the sedan down, arrests the driver but there's no TM and the dude is not cooperating. To me, this validates what the eyewitnesses saw. If they had the wrong guy, there's no way the man in custody would not cooperate & give them all sorts of information they could verify to prove he's not their guy. The fact that he's not cooperating ("zero" was the officer's answer to the reporter's question on the suspect's level of cooperation) tells me the CPS had to have either accessed his phone (pings), his car's GPS logs (if it has one) or have had other witnesses who saw that sedan on one of those roads out there. I'm thinking it's probably his phone, but I'm just guessing.