Lookup with search range start based on position of last blank lin

[rcmodelr]

Here is some sample data...

A B C D E
Arr. Trk
Lot time Grower No. Driver
r2 Mary
1:00 Odom
2:00 Jesse
2:00 3:00 Odom
2:00 4:00 Jesse
a1 Total

a2 Lingo
2:00 5:00 Odom
2:00 6:00 Jesse
2:00 7:00 Odom
2:00 8:00 Jesse
a2 Total

Column A contains Lot number and calculated turnaround time for each driver.

However, with second farm drivers come from, first load should NOT have a
calculated turnaround time.

Is there some way I can set the start of the lookup range to be the cell
address of the last blank (null) entry in the E column so the formula will
NOT look into the data from the previous farm when calculating the individual
driver turn-around time?

Here is formula used in A column currently to calculate turn-around time
with arrival times entered in 12 hour format (NO AM/PM). Formula below
copied from A column first load data line from second farm, Row 17. Same
formula copied into A column for EVERY row that will contain driver and load
data.


=IF(OR(E17="",ISNA(LOOKUP(2,1/(E8:E16=E17),B8:B16))),"",IF(B17>LOOKUP(2,1/(E8:E16=E17),B8:B16),B17-LOOKUP(2,1/(E8:E16=E17),B8:B16),(B17+TIME(12,0,0))-LOOKUP(2,1/(E8:E16=E17),B8:B16)))

First IF handles error trapping so A remains blank if no data, or no
matching data found in E column. Second IF handles error trapping to adjust
if current arrival time value is less than previous arrival time value for
this driver.