。
I need more time.
Literal
More time [subject-が] necessary [copula-だ].
必要 ('necessary, needed') is a na-adjective whose object is marked with が, not を — like 好き, 嫌い, 上手. Literally 'more time is necessary.' Also note もっと, the all-purpose 'more' adverb. A short, useful sentence.