Is it permissible to combine the Sunan prayers at the end of the day?

The Prophet's guidance (peace be upon him) was to consistently perform the regular Sunnah prayers at their prescribed times. If someone misses the pre- or post-Dhuhr Sunnah until the time for Asr prayer begins, the Sunnah is to make it up after performing the obligatory Asr prayer. However, delaying a regular Sunnah prayer beyond its time to perform it at a later time was not part of the Prophet's guidance (peace be upon him).