Good morning,
Thanks for getting in touch 🙂
The visa pack will be sent to you 15 weeks before your departure date. When you receive the visa pack you can send it back to us and we can start the visa process. The visa for Cambodia can't be applied by us, more than 3 months before the return date of the holiday or it won't be valid. Currently the visa applications for this tour is taking approximately 5 weeks. So i think you will absolutely fine to use your passport over Christmas,
Kindest,
Ben