The official answer is that a Level 3 purge should take about 45 minutes to complete. Be warned, if you've scheduled people to come move your printer, your printer might be a wise ass and display a message like "consumables need replacing, call Canon for service" (you can't execute a purge until this warning is cleared). This isn't mentioned anywhere in the manual and if you've paid someone to show up at a certain time, this could end up costing you $$$ (far more than it should already cost just to move the darn thing down 2 flights of stairs). Canon was no help here (and I wasn't about to pay them $1500 bucks to come out on top of the $771 bucks worth of ink and the $270 worth of maintenance carts just so I could move the printer down a few flights of stairs) but there's a work around if you have someone showing up at your door and you need to continue with the purge.
You can bypass this message by going into service mode by holding down the navigate and load buttons whilst turning on the machine, until an 's' appears in the display. From there go to the maintenance menu, click OK, select service mode, click okay, click the right arrow until the display reads "INITIALIZE" ***then click the down arrow***, click the right button until the display reads "PARTS COUNTER", again click the down arrow, and now you can reset the counters allowing you to continue with your purge.
I wasn't about to lose my deposit on the movers because of Canon's inability to warn people that this might happen in the section of the manual dedicated to moving the blasted thing. Had they mentioned it, I would have planned (and cursed) accordingly. The following things are listed as "consumables":
3 different waste ink absorber units, suction fan, duct, carriage, mount sensor adjusting, scale linear, tube unit, multi-sensor unit, purge unit, sensor, motor carriage, feed motor assembly, fan unit. Then of course there's heads, ink and maintenance carts.
Seems like an awful lot of things that shouldn't be consumable are categorized as consumable. :-( (curious to know how this compares to Epson). Looks like the service manual is up on the Canon Wiki:
http://canonipf.wikispaces.com/file/view/ipf8300+Service+Manual.pdfCheers, Joe