If you're making changes to your fixed-date or contact date property based workflow, you may notice that you are unable to change the timing of one of your delays. This happens if the attempted change will cause the delay to be out of order in the workflow.
For example, you have a workflow that centers around the date January 24, 2018.
The first delay is set for two days after January 24, 2018 at 12:00 PM. If you attempt to add a second delay, you will be unable to set the time of the delay to anything prior to two days after January 24, 2018 at 12:00 PM, as this would put these delays out of order.
The same is true if you're trying to edit a delay to make it occur later. If the attempted edit would set the delay for a later time than another action further along in the workflow, you will not be able to make the change.