I need to determine whether train cafe's are opening on time. There is currently no data that can tell me the opening time. I do have data that shows me the point of sale details including date and time of the first item sold in the cafe's. i have the train schedule which has the scheduled departure time and location for each of the relevant trains. Given the lack of data to tell me this info, what is the best way to estimate the opening tome of the cafe with what i do have?