勤務, 通勤, and 出勤: work and the journey to work
Compare hospital employment, a request to change working hours, a train commute, and going to work on a particular day. Separate work relationships from travel intervals.
勤務: employment and working hours
勤務 (きんむ) means work or employment. 「姉は町の病院に勤務している。」 describes the older sister working at the village hospital. It identifies her employment relationship rather than only a scene of travel.
「勤務時間を変更する申請を出した。」 reports submitting a request to change working hours. The requested change concerns work time; submission does not establish approval of the change.
通勤: the recurring journey
通勤 (つうきん) means commuting. 「毎朝電車で会社へ通勤している。」 specifies a recurring morning journey to the company by train. The destination and transport are stated.
「通勤に一時間かかるので早く家を出る。」 relates leaving home early to a one-hour commute. The hour belongs to the journey, not to time spent working at the company.
出勤: a particular journey to work
出勤 (しゅっきん) concerns going or reporting to work. 「今朝はいつもより早く出勤した。」 reports going to work earlier than usual this morning. Read that day's action and timing.
「雪の日は出勤に普段の倍の時間がかかった。」 identifies a journey to work on a snowy day that took twice the usual time. Read that travel interval without extending it into a rule for every snowy day or an increase in working hours.
What information differs between hospital 勤務, a daily train 通勤, and going to work early today through 出勤?
Show the answer and why
They describe the employment relationship, the recurring train commute, and today's action of going to work. All can apply to one person, while the relationship, travel interval, and particular day's action remain distinct.