It's essential to make the best possible use of the time we're given.
Literal
Given [attributive-の] time [object-を] as-much-as-possible make-use-of [thing-こと] [subject-が] necessary is.
与えられた時間 ('the given time') is a passive relative clause — the perfect tense construction Japanese lacks gets filled in by context. 利用する ('to use / make use of'). ~ことが必要 ('X is necessary') is the standard 'X must be done' abstract framing.