Evri have published their posting deadlines for sending parcels in the UK:

• Friday 20th December – For Standard delivery: parcel drop off by 11am at a ParcelShop 
• Saturday 21st December – For Next Day delivery: parcel drop off by 11am at a ParcelShop 

Evri also recommend you keep an eye on their Service Status Page. It will be updated over the next few weeks so you can find out if there are any issues such as adverse weather impacting their service in your area.