A slot does not overlap with another if it ends before the other starts, or it starts after the other ends.
where '11:55' < StartTime or EndTime < '10:00'
To find overlapping slots, invert the rule. It ends after the other starts and it starts before the other ends.
where StartTime < '11:55' and '10:00' < EndTime
There’s no need to cast the values, MySQL will do it for you, assuming StartTime and EndTime are time columns.
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