This is a good question. By the time the police arrived (and surely spoke directly with the neighbor, who was almost certainly waiting for them), it was known by the neighbor that Suzanne's car was in the garage. I believe the neighbor had been told by a family member that Suzanne might be on a bike ride. Did police look through the garage window? Did the neighbor?
Did police merely knock on the door and circle the house, to see if there was movement? Finding no response, did they find probable cause to use locksmith tools to open the house? Did they speak to the family during this? (Probably). This was basically a welfare check, woman is not where family expected her to be, is concerned enough to ask neighbor to go over and then to have neighbor call police.
If they did go in, at that point, they touched nothing and simply walked around, making sure she wasn't unconscious on the floor somewhere.
What then? Noting the absence of the bike and the family's belief that she was on a bike ride, they fanned out, calling in more help, and looked around the house but also on the likely path she took with her bike. Who found the bike?? We don't know.
At 9 pm or thereabouts, Barry arrives and if LE hadn't already gone into the house (surely they had?) they would then go in, and perhaps accompany Barry while he looks in closets. They would have asked a lot of questions about her mental health, her physical health, whether she took medications and whether she left the house with or without certain items (meds, phone). It must have looked like a bike ride gone wrong, that night. Pictures were taken of the bike and its surroundings. Next day, they go back out and do the grid search (one of several).
We do not know if or when the daughters arrived home. We don't know if BM was barred from the house that first night or not. We do know bodies of water were searched, indicative of a fear of suicide, homicide or serious misadventure (because the creek right where the bike was...wasn't particularly conducive to either homicide or suicide by water). But the catchment area behind the dam (the big pond) would be, so it was searched. Searches in the water were probably repeated, and I'd assume they would have brought in cadaver dogs after 5-6 days.