Can I set up an automation to fire 24 hours after the date set up in a custom date ticket field?
No. The conditions Is within the previous and Is within the next take an integer number of days, that translate into multiples of 24 hours. The automation looks back or forward 24 hours to determine if the ticket’s custom date field is in that window, but it will not wait 24 exact hours to take actions.
At the same time, automations use UTC timestamps for custom date field conditions. Since they don't use the account's local time zone, this may lead to appear that automations fire several hours early or late, depending on how far the account is from UTC.
For more information, see these articles: