Check for time conflicts in your class schedule.
Two classes overlap by the later of their start times subtracted from the earlier of their end times, floored at zero. A zero overlap is necessary but not sufficient: a schedule with back-to-back classes in buildings ten minutes apart is a clash in practice even though the timetable shows none. Subtracting travel time from the gap gives the figure that determines whether the combination is actually attendable.
Overlap
Overlap = max(0, min(end A, end B) - max(start A, start B))
Feasibility
Spare time = gap between classes - travel minutes required
At least the walking time plus five minutes. Lectures routinely overrun by a couple of minutes and corridors are congested at changeover, so a zero-buffer schedule means arriving late repeatedly.
This compares two sessions on the same day. Sessions on different days never clash regardless of time, so check each shared day separately.