As a course lecturer, should I excuse late assignment submissions if I wrote the assignment deadline slightly wrong?
If the assignment deadline was not shown correctly to the students, then it is your error and they cannot be penalized for being late.

Claiming it is correct in one area while incorrect in another does not absolve you, you caused the confusion so you have to accept late submissions, as long as they arrived on Saturday...

Any submissions on Sunday will, of course, be late.

Re-reading this, it sounds a bit blunt... Probably because I have done exactly the same and had to sort it out after... Peace reigns if you stick to being fair, so giving them the extra time does not usually make much of a difference, except for the recognition from the students.