Do not take too many chances when you drive at night.

Question

I know too is an adverb modifying many an adjective
I know when is an adverb. Does it modify drive?

Answer 1

"when" is the introductory word for the dependent clause "when you drive at night."

That dependent clause as a whole modifies the verb, "do take"

Answer 2

Yes, "too" is an adverb modifying "many."

"When" introduces the adverb clause, "when you drive at night." The clause modifies "do drive."

Also -- "not" is an adverb modifying the verb "do take."