The に particle can be used to mark a particular time as a target—creating an absolute time expression.1
Example: On Tuesday I will eat cake
火曜日にケーキを食べる
Info
火曜日 (Tuesday) is the absolute time expression. It is marked by に, making this date the target.
ケーキ (cake) is the を marked object.
が is not present/visible, so the core subject is assumed to be わたし (I).
食べる (will eat) is the verb.
