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