The -Xmin and -Xtime flags match files accessed (a), had their contents modified (m), or had their inode changed (c) n minutes (-Xmin) or days (-Xtime) ago.
All mtime changes are ctime changes, but the reverse is not necessarily true.
Prefix n with + or - to match files strictly before or after the specified time in the past.
For example:
# Matches files accessed *more* than 30 minutes ago
#
find . -type f -amin +30
# Matches files modified *less* than 7 days ago
#
find . -type f -mtime -7
# Matches files modified *today*
#
find . -type f -mtime 0