I May Be a Guild Receptionist, but I'll Solo Any Boss to Clock Out on Time, Vol. 3 (light novel) — Mato Kousaka

Despite her best efforts to avoid doing so, Alina Clover finds herself sneaking off in the night yet again to smash monsters (and walls) in dungeons to cut down on her overtime. But a glimmer of hope emerges when Alina learns of a new policy being implemented at the reception counter: Employees who submit a compelling operational improvement plan will be given a day off on their birthday. Now Alina is fixated on getting that birthday break…even though she's totally stumped for ideas to propose!