Amar ensured the timely delivery of the products.

In the sentence 'Amar ensured the timely delivery of the products', the word 'timely' describes the noun 'delivery', telling what kind of delivery it was - one that was on time. Words that describe or modify nouns are adjectives. Although 'timely' ends in -ly (which usually indicates adverbs), in this case it functions as an adjective modifying 'delivery'. Therefore, the correct word class is adjective.