Сейчас у меня есть мало времени
is correct as already pointed out.
In this sentence Genitive case stems from the relationship between the pronoun мало and the noun время and not from the verb есть.
So without the pronoun the case is Nominal as expected
У меня есть время
However with the pronoun мало, which is the subject of the sentence, the Genitive form of время -> времени answers the question (мало) чего? - (a little) of what?
Likewise with other quantitative pronouns много, немного, немало, столько, несколько, сколько?, also чуть-чуть and полно́ which function as pronouns, and synonyms of those.