Option A - 'Many' is a determiner, which is used with countable subjects only. As 'time' is uncountable, we can't use 'many'. Thus option A is incorrect.
Option C - 'Few' is a determiner, which means 'not many'. As the sentence is already negative, we can't use a negative determiner. It is used with countable nouns only. As we can't count 'time', 'few' is the wrong choice. Hence, option C is incorrect.
Option D - 'Little' is a determiner, which means 'not much'. As the sentence is already negative, we can't use a negative determiner. It is used with uncountable nouns, but as the sentence has 'isn't' we can't use 'little'. If the sentence had 'is', we could have used 'little' then. Hence, option D is incorrect.
Option B - 'Much' is a determiner which is used in a negative sentence. It is used with uncountable nouns. Hence, we can say 'there isn't much...' Thus option B is the correct answer.
'There isn't much time before the celebrations start.'