I always change the date to the correct one. If fact, I make a point to log them in the exact order I found them. On several days while logging a higher number of caches, which is about 20-25 for me, I missed a log and have had to copy all my logs to notepad, delete those logs, and then re-submit them in their correct order. I guess we all have our quirks, that's mine. Well, of of many...
I have seen logs from others dated a long ways off from the actual find date. When Tat logged
Cache Like It's 2001 (GC146JV) by
Sudonim (5/5) with a date of Nov 2001, almost 6 years before the cache was placed!