All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If a person who is performing Hajj or 'Umrah delays shaving or trimming his hair until he returns to his country, he is obliged to offer a sacrifice according to the Hanafi and Maaliki scholars contrarily to the view of the Shaafi'i and Hanbali Schools, but one is not obliged to offer a sacrifice if he delayed cutting or shaving his hair because he forgot or he does not know the ruling.
However, it is better for a person performing 'Umrah to shave or trim his hair just after finishing his 'Umrah, and he should do so in Makkah, in order to avoid the difference of opinion, and this is hasting to fulfilling the Commands of Allaah and being acquitted.
Nonetheless, if a person who performs 'Umrah is not able to shave or trim his hair due to the lack of time, as the questioner mentioned, then he may shave or trim his hair at any place inside the boundaries of Al-Harram area surrounding Makkah [the sacred precincts of Makkah lies between At-Tan'eem-north, Adhaah-south, Al-Jiraanah-east and Ash-Shumaysi-west], then he may travel afterwards.
For more benefit, please refer to Fatwa 84306.
Allaah Knows best.