Times are stored internally in Excel as fractions of a 24-hour day, and
fractions are notoriously difficult to get an exact match on them due
to rounding errors - your two values of 9:30:55 AM may look the same,
but there may be differences in the 10th or lower decimal places. You
could amend your table to this, by multiplying the time column by
24*60*60 (and thus convert the time to integer seconds):


9:30:55 AM 34255 440.43
9:30:56 AM 34256 440.22
9:30:57 AM 34257 440.03
9:30:58 AM 34258 440.44
9:30:59 AM 34259 440.06
9:31:00 AM 34260 9999

and then amend your formula to:

=VLOOKUP(R617*24*60*60;table2;2;false)

where table2 would now be from B1 to C6 instead of A1:B6 (or wherever).

Hope this helps.

Pete