When do technical and medical checks take place?

Checks take place on Sundays at the Hotel Playitas from 2 p.m. to 10 p.m. (final arrival time for participants). You must show up with your medical certificate and all of your equipment and food that you have planned for the 4 days of racing, according to the official Half MDS rules and the mandatory equipment list. 
https://www.halfmarathondessables.com/equipment#mandatory-equipment