Did she say when they had left? I couldn't find that, just that they had left for holidays and 20 minutes later the police showed up at the house. If they did leave on the Friday night it seems odd, why leave so late with a little one in tow? And how then did MS excuse himself to dispose of the body? ...not expecting you to have the answers by the way!
Neighbour said MS and family left about 20 minutes before police arrived at their house.
The call to the police from the hospital colleague re SE was at 7.20pm. So allow for police to first check SEs house, to be sure she is not there, then the visit to MS would probably be 8pm or thereabouts.
Possible scenario. MS and family depart for holiday ( I do think this was planned, due to roof box being put in place Thursday night ).
Wife and child in car, MS in van. All drive to g/mother house, to leave van on driveway ( probably usual procedure when going away ).
Then, instead of getting into car, MS tells wife there is a sudden emergency. Tells her to drive on to holiday venue ( probably Peak District or similar, only 40 mins drive away ) and says he will come along later.
This effectively means wife and child out of way - leaves MS free to drive to quarry at the right time as its getting dark.
After burial, returns either to own house or parents, calls or texts wife, says too late to drive to holiday venue now, will travel Saturday AM. Probably wants to clean van and recover from what he has had to do.
Then of course Saturday AM, news is everywhere re SE disappearance, so MS stays in Stoke to help with search and wife/child drive back home.