How to fixed date & time format conditionally

If cell A1:A having text like (blank), then cell B1:B will be current date – 1 space 23:59 (example: 2/23/2013 23:39 ).
Please remember that always date & time format will be MM/DD/YYYY HH:MM
My actual data like following

CELL A               CELL B
2/20/2013 6:57	2/20/2013 6:57
(blank)	        2/23/2013 11:33
2/20/2013 8:05	2/20/2013 8:05

I need to convert like below

CELL A               CELL B
2/20/2013 6:57	2/20/2013 6:57
(blank)	        2/23/2013 23:59
2/20/2013 8:05	2/20/2013 8:05

I have tried something like below formula

B1=IF(A1="(blank)",NOW()-1,A1)
B2=IF(A2="(blank)",NOW()-1,A2) ' here i want to keep current date-1 23:59
B3=IF(A3="(blank)",NOW()-1,A3)
..............................

Hi, dilipandey, thanks for mail, it is not correct please check below comments
"(blank)" is not actually blank, it is text(7 characters text data ), so don't treat it as blank

Hi, dilipandey,
I got your point, Many thanks for helping me , it is something like

B1=IF(A1="(blank)",TODAY()-1+TIME(23,59,0),A1)

hi, SDCh thanks