turn down logging levels in dates.py

[melange396]

after a reasonable amount of time or when our curiosity has been sated, change the logging levels in dates.py to DEBUG. this applies particularly to the lines added in #1027, and should include the 5 INFO level calls and probably the one ERROR level call too.

the information logged here is potentially interesting, but ultimately not super useful nor something we need to keep adding to our production log footprint.