"find -mtime +1" will return all files with modification times more than 24 hours ago, i.e., everything
not modified in the last 24 hours.
The description for the "+" and "-" signs is near the top of the "TESTS" section of the manpage:
Numeric arguments can be specified as
+n for greater than n,
-n for less than n,
n for exactly n.
What you want is "-mtime -2" for files modified less than 2*24 hours ago.