Hi, nemeseri. Iíve climbed Shasta 34 times by six different routes and Whitney 36 times by five different routes. This includes at least one dayhike on each peak in each month of the year.
Snow conditions and weather can make a huge difference, but everything Steve said is correct. A dayhike on the Mountaineersí Route should take less time than Avalanche Gulch. However, the MR is harder in a couple of ways:
First, itís almost impossible to get lost on AG in decent weather during daylight hours. The MR is a bit trickier. If the Ebersbacher ledges are free of ice and have little or no snow, go that way. Otherwise, youíll follow boot tracks up the left side to LBSL. You should be able to follow boot tracks pretty much all the way up, but some of those tracks will be totally wrong, so study the route descriptions carefully.
I think the MR is technically more difficult than AG. The snow in the chute is steeper. The final 400 may have water ice, and it will probably require a little rock climbing with your crampons. The easy walk-off may have loose, deep, avalanche-prone snow, so you canít know in advance which variation is better.
If the weather is good, and you arenít obsessed with summiting, you should be fine.