I've been doing it for an hour on 4 toons now and I can say that doing it on multiple characters is only somewhat slower than a solo character. Using the windrider system I can basically always have guys on the flight path to their next dig site while I'm actually doing the nitty gritty at digsites on a toon. It's tedious but if I only have to do this for 40 hours to get 4x Zin'rokh I'm sold