I am not sure which is the visa office for your friend. I can share my experience of sending passports to ADVO. If everything goes fine, it should take about ten days from sending to receiving back passport from Riyadh to Abu Dhabi. ADVO takes around three days for its internal processing while the other seven days are for shipment by Aramex courier. The good thing is that Aramex also delivers visa-stamped passports to the applicants on Saturdays.
So your friend can give the passport to the courier on the first day of his 29 day stay in Saudi (preferably a Sunday morning to get the passports on the way as soon as possible). Hopefully, he should get it back on the 11th day with visa stamped. Needless to say, the guy will be very nervous throughout.