Here's Query3 from the database presented a little more cleary, also with GapMins column added.
SELECT a.WorkerID
, a.WorkDate
, DateAdd("n", 1, a.EndTime) AS GapStart
, Nz(DateAdd("n", -1, min(c.StartTime)), b.LatestEndTime) AS GapEnd
, DateDiff("n", DateAdd("n", 1...