Start Time and End Time
Appoint time slot N from start time N to end time N. N ranges from 1 to 3, thus there are three time slots in a day. Time format is hh:mm, hh is Hour (0-23), while mm is minute (0-59). End time must be later than or equal to start time in the same time slot. When start time equal to end time, it shows the time slot is unusable.

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