I had to use the Format function as subtracting some Singles or Doubles can
cause problems like:
Debug.Print  55567.3 - 55555.5  =  11.8000000000029

If you are just using integers, you won't need it.

SELECT Format(LR.LastRun-NextLastRun,  "0.00") AS NetHours
FROM
 [SELECT TOP 1 tblDates.wa_date,
         tblDates.HoursRun as LastRun
  FROM tblDates
  ORDER BY tblDates.wa_date DESC]. AS LR,
 [SELECT TOP 1 tblDates.wa_date,
         tblDates.HoursRun as NextLastRun
  FROM tblDates
  WHERE tblDates.wa_date <>
       (SELECT TOP 1 tblDates.wa_date
          FROM tblDates
      ORDER BY tblDates.wa_date DESC)
ORDER BY tblDates.wa_date DESC]. AS NLR;