I appreciate the suggestions to make the sheet auto recalc, but this is not
the solution. It is in auto recalc mode. Even doing a manual recalc mode
will not do the trick.

Here's the formula: =F3+TIMEVALUE("05:00 PM") where F3 is a day entered by
the user. On Sunday morning, after the time change, this formula returned an
error, causing other formulas depending on it to return "time is invalid".
But when I copied the cell and pasted it's value in another cell, it was
correct.