please rephrase your question.  I'm afraid I don't follow what you are asking.

In Access a single field holds a date and time together. To which lesson are you referring? Time index?

sure, sorry for misunderstanding

if the data type date/time was used to store only date information for example short date. so no timing information stored at all.
so no need for date+1 or date-1 to include the whole date as there is timing issues.

in this case, because no timing issues, we don't need to declare the parameter. we simply can enter just one parameter [enter the date]. and that's it.

but if there is time information stored and we need to write the same parameter [enter the date] two times, so here we need to declare the parameter.

in brief my issue is the time. i hope it is clear. if not, no worries i am sure more classes coming will clear many ideas.

You are correct. If you're dealing with, say, OrderDate, and the user isn't entering in a time component, then you don't need a range. This video might help you: Between