Here is my opinion:
You should follow the dosing schedule as close as possible. Sudden changes in the levels in the tank of what is needed by the plants can lead to algae problems.
"missing an occasional dosing" will not "cause" your aquarium any problems, but if it happens often you might.
If you miss the dose in the morning, just dose in the afternoon/evening, just try and dose on schedule. It is not the time that matter as much as the day for EI.
3 days a week for Macros, 3 days a week for Micros, and water changes.
If you miss two days, just dose what ever you should have dose in the first day and start the schedule again from there.
M - Trace
T - Macro
W - Trace
Th - Macro
Sun - water change and Trace
If you missed Thursday and Friday, then Saturday just dose Macro as usually and continue on.
If unable to do my usual 50% water change on Sunday just do on Saturday or Monday. What is important is doing the water changes to balance thing back to a base level and get rid of the bad.
From the above example if my water changes are on Sunday and I do it on Saturday instead, I just do the water change then dose the Macro as I would usually dose on Saturday and then the Trace on Sunday.
EI method is an easy one. Give the plants what they need in excess so they never run out, and then do water changes to bring back to base level.