# A scheduled maintenance once per day at around midnight?

I have to describe that a certain process happens once every 24 hours at around midnight (before 23:59:59). What is the correct usage?

1. "once per day at around midnight"
2. "daily at around midnight"
3. "once per night"
4. "nightly"

EDIT

After seeing Jim's answer, I have amended the question to "at around midnight" from "at midnight" as that was my original need

• Maintenance is not ordinarily countable, so a maintenance sounds a bit strange. You can have scheduled maintenance, or a scheduled maintenance task, job, run, process, etc. – choster Jun 20 '17 at 14:22
• "Every 24 hours at around midnight" seemed clear enough to me. (Or "just before midnight", if that's important.) – calum_b Jun 20 '17 at 16:45

First, note that "at midnight" and "before 23:59:59" are mutually exclusive. Midnight is at 00:00:00, just after 23:59:59!

I would say that the first two instructions would be correct, i.e. "once per day at midnight" and "daily at midnight" are equally clear and largely unambiguous. If we want to be clear that the event happens at precisely midnight without variation, we could put "precisely midnight" or "exactly midnight". If the event happens at midnight, plus or minus, we could put "about midnight".

"Once per night" or "nightly" would imply that the process happens at some ambiguous point during the night. This could be 8 pm or 4 am or midnight - we simply can't tell. We also can't tell if the event happens at the same time each night; the time could vary and the description here could still be apt.

If the event happens each night at the same time but not specifically at midnight, we can say exactly that: "Once per night at the same time".

Which style to use depends on your level of pedantry and your need to be precise. If this is some sort of technical or academic writing, accuracy is likely more important than the risk of pedantics.

• meant to write "around midnight", I have amended the question – senseiwu Jun 20 '17 at 13:28
• About your first note - technically, the day before the second after still counts as "before 23:59:59". The midnight you mentioned is probably the one they meant, though. :) – Lawrence Jun 20 '17 at 13:28
• My examples still hold. "Around midnight" or "about midnight" both imply that the event happens at midnight, plus or minus some unknown varying amount of time. You could put "near midnight" or "close to midnight" to imply that the variance is small, if this is the case. – Jim MacKenzie Jun 20 '17 at 13:32
• It occurred to me later that your task/job might need to be run prior to and not after midnight, so this might take some massaging of the language to make clear. Also, depending on the task's duration, is it important that it ends before midnight or only that it begins before midnight? If these are important issues to this situation, that will affect how we word the description. – Jim MacKenzie Jun 20 '17 at 14:37