Match the window before the distance.
Agree whether the useful overlap sits around a central workday or a Slough-side routine before choosing a broad area.
Starting around London
At the London end, use “Availability may be tied to the working day in one place and home routines in the other.” as a scheduling prompt rather than a claim that the whole route is local.
Planning around Slough
At the Slough end, agree whether the useful overlap sits around a central workday or a Slough-side routine before choosing a broad area.
Compare both local pages
Treat each town as a separate local context, then use the overlap planner rather than assuming the full route is convenient at every time of day.