Praise be to Allah.
The Prophet (peace and blessings of Allaah be upon him) encouraged us to perform ‘Umrah in the month of Ramadaan. Al-Bukhaari (1782) and Muslim (1256) narrated that Ibn ‘Abbaas said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “ ‘Umrah in Ramadaan is equivalent to Hajj.”
This includes all of Ramadaan, not just the last ten days.
And Allaah knows best.