not sure what you mean by Mantid Exchange, so you turn in the artifacts for crates that have Tol'vir artifacts? if so then I get it, if not then I am lost
(if any of these numbers seem wrong, let me know, i will edit them. it's mostly from my memory of how long each task takes, it's probably way off)
Crated Artifacts:
35-45 mantid fragments = 1 solved artifact = 1 crated artifact = 7 tolvir fragments.
my approximation of the mantid collection speed is maybe ... 7 minutes from site collection + movement to the new site + combat with mobs in the area (especially dread wastes, or klaxxi areas)
so you can crate a mantid item in 21 minutes or so. an average of 5 crated artifacts will solve 1 tol'vir artifact, which may take under 2 hours.
Time:
if you can move and loot 30 sites in 2 hours, you can collect 200~280 fragments, and convert the solved items to 9 crates.
but your speed may vary. the key is to get a count of how many solved artifacts as crates, in a 2 hour stretch.
Using, and buying the MASL doubles the return rate, as it doubles the number of farmable zones in one area.
if it takes 15 mantid sites, or 25 mantid sites to get 5 crates, then, again, the question is how long does it take to get the 5 crates, to get a tolvir solve ? what would be the minimum time it has ever taken to get 5 crates. use that as a baseline, for 1 tol'vir solve.
I assume it takes in the region of 8 mantid areas in an hour, with killing adds and other things. You can probably get 9 to 10 crates in 2 hours just cycling mantid solves and the 2 spare crates for the artifact hunter kit, with the MASL, and lorewalker map, that will reset locations every so often. but you may only be getting 4 sites per hour, up to 12 per hour, depending on the zone and the luck/RNG of the day.
The Old System:
prior to MoP, The tol'vir appearance rate is normally 1 site every hour, and you used to get upwards of 10 sites/hour with the MASL and the old exploit. which meant more than 3 or 4 tolvir items an hour, instead of 1 every 40 minutes (give or take) there's a lot to be said about the advantage of using the 24 hour long exploit / quirk of the old MASL, it was, between 2x to 3x faster than the original mantid solves, because of the extra time and distance of travel needed to reset the tol'vir sites and deal with the CRZ pauses. you could collect in the region of 100 fragments an hour or so. which is 3 solves. of course, this is all from memory and napkin math, and it doesn't account for the key's/tolvir hieroglyphic that drops along the way for reducing the 35+ fragment items back to 40 or so fragments.