Shankar for past 2 years I have been lucky to have seen tigers and sometimes leopards almost in every trip and missed out on few occasions. As a thumb rule sightings of predators are better in the evening, however I have seen tigers both during morning and evening safaris. In winters it is good to spot a tiger in the morning as the light is better.
It is advisable to do min 4 safari rides to spot a tiger, again it depends on your luck too