No, you can use a date/time string.
From man find:
-newerXY reference
Compares the timestamp of the current file with reference. The reference argument is normally the name of a file (and one of its timestamps is used for the comparison) but it may also be a string describing an absolute time. X and Y are placeholders for other letters, and these letters select which time belonging to how reference is used for the comparison.a The access time of the file reference B The birth time of the file reference c The inode status change time of reference m The modification time of the file reference t reference is interpreted directly as a time
Example:
find -newermt "mar 03, 2010" -lsfind -newermt yesterday -lsfind -newermt "mar 03, 2010 09:00" -not -newermt "mar 11, 2010" -ls