Hi,

Use this formula for conditional formatting:
=IF(TEXT(NOW(), "ddd") = C$2,
IF(AND(TIME(HOUR(NOW()),MINUTE(NOW()),SECOND(NOW() ))=$A3,
TIME(HOUR(NOW()),MINUTE(NOW()),SECOND(NOW()))<$B3) , 1, 0), 0)

In this formula
Column A is start time
Column B is the end time
Row 2 is the day

ie
C2 is today's date abbreviated to 3 characters
A3 is start time
B3 is end time

Hope that helped.

Shafiee.