When he realized he was going to be late for his exam, Watson is jumping out of bed and searched for his bag.

Correct sentence: When he realized he was going to be late for his exam, Watson jumped out of bed and searched for his bag.

In this sentence, the verb "realized" is written in the past simple tense. Therefore, the verb "jump" should also be written in the past simple tense as "jumped."

It took the family members over three hours to find Jerry, who will hide behind the giant bushes after hearing the scary sound.

Correct sentence: It took the family members over three hours to find Jerry, who had been hiding behind the giant bushes after hearing the scary sound.

In this case, past perfect progressive form "had been hiding" makes sense, as the hiding has already taken place and describes how Jerry had hidden for some extended period of time.

If you score good marks in exams, it leads to many opportunities.

Correct sentence: If you score good marks in exams, it may lead to many opportunities.

In this case, the word "may" properly reflects the possibility that a perfect score can lead to many opportunities. It would not be appropriate to use any forms of the past tense of the verb "lead".