ah, this is a little more tricky being the last 30 days...
add something like:
AND
(
LTRIM(MONTH(FMC_AvailabilityByDays.datetime)) = (LTRIM(MONTH(getdate())) -1)
AND
DATEPART(dw, FMC_AvailabilityByDays.datetime) between 2 and 6 --- gives monday through friday
AND
( --- gives btn 6a and 11p
t.DateTime BETWEEN
CAST(Convert(Char(10), FMC_AvailabilityByDays.datetime, 101) as smalldatetime) + ' 06:00'
AND
CAST(Convert(Char(10), FMC_AvailabilityByDays.datetime, 101) as smalldatetime) + ' 23:00'
)
)