Here's a benchmark for you.
I have a Kubota B7510HST (21 HP engine) with an LA302 FEL (48" wide) and a KK box blade (also 48" wide).
Last week I excavated a path for a paver block walkway from the driveway to the front porch steps, about 4.5 ft wide x 70 ft long and 6" deep.
Used the box blade with the scarifiers all the way down to loosen the soil, which was really damp because of all the rain we've had here in the North Valley.
Then I used the FEL with a Markham toothbar to dig the rest of the way. Took me about 2.5 hours to get it the way I wanted it.
Last April I had a driveway installed (20 ft wide, 260 ft long with 6" thick roadbase gravel). The contractor used a JD 210LE tractor (73 net HP, 86" wide) with FEL and a box blade with hydraulic scarifiers. Took Mike, the operator, about 90 minutes to do the excavation. The ground was soft enough and the box blade was a heavy beast, so he didn't have to use the scarifiers.
Looks to me like you have an all-day job ahead of you with your CUT.