Mag. It's called a mag.
I prefer clip as I was brought up with Doom.
Keep in mind the turns overlap, with the same close combats happening in both player's turns and fliers 'stopping' mid-air while the opponent reacts to them. While player turns can almost represent a simultaneous timeline, the whole game would make sense that it spans about 10-20 minutes of real time.
We're playing skirmishes, like Serp said. Now apocalypse games...
Why would apocalypse change anything? All it means is that more things happen at the same time, having 1 person taking 10 steps does not take any longer than having 1000 people do the same thing simultaneously.
10-20 minutes is a very long time. If you used 5 game turn and walked 6" each turn for a total of 30", then translated that into a real world measurement would it really take you 5-10 min (using half your allotted time as it would refer to a single player) to walk that distance? I dont know the exact measurements but I'd guess it's somewhere around 30 yards/meters in length. 1" on the tabletop does seem like 1 yard or meter though scale is a bit morphed due to heroic scale. You could assume a guardsman is pretty accurate to real world size though.
Did some googling and found that the length of a Leman Russ hull length is 4.5" and the official metric measurement for the same area is 7.08 meters. This translates into 1.57meters per inch on the tabletop. Then again the tabletop version of the Leman Russ might just not be to scale.
Anyways, 30" on the tabletop with the above measurements would be 47.2 meters or 51yards. If you walk an average of 4Km/h or 1.1m/sec it would take you 27.3 seconds to walk this distance or 5.45 seconds to walk 6" per turn. Pretty close to my own estimate
Checking wiki it seems walking 4km per hour is something old people manage, 5.32-5-43 is the average for younger individuals (which I would guess applies to combat trained people, and this is walking not dashing from cover to cover).
With an average of 5.35km/h you get 1.49m/s, or 20.1seconds to walk the 30", 4s to walk 6" per turn.
From my calculations I'd guess the movement phase lasts about 5 seconds.