Also, I believe BM was calling SM not to give her a warning, but to make sure she was home. IMO, he had already decided that he was going to carry out his plan - exactly when, I don't know. Friday? Saturday morning? I think that's why he was so anxious and antsy all morning and sent MG home early. I'm with
@mrjitty that perhaps his original plan was to kill her Saturday night before he left for Bloomfield. But I believe he was anxious about it and just decided to get it over with. Moving up his timeline. So once he made up his mind he was frantic to make sure she hadn't left - either on a bike ride...or forever. I know I'm in the minority but I don't believe that BM saw a text to JL from SM and snapped - just that day, having no thoughts of murder ever. No, he had made up his mind well before Saturday - it was just a question of when.
Im super interested in questions that establish the when of premeditation:
When and by whom was the girls' camping trip setup and decided upon?
When was each hotel room reserved in Broomfield?
All just my opinions.