When I power walk, on the treadmill, between 6-7 miles total, at speeds of 5 - 5.4 mph, with maybe incline intervals for extra cardio boost, then yes, I consider that my workout for the day.
It all depends on what time you have available, what your goals are, where your energy levels are at, and how easily your boredom threshold is reached. I can't workout more than once per day. I get bored too easily, plus there's just too many other demands from family upon my time.
Go in, work out as hard as you can, get out and be satisfied that you have done your workout for the day. That's my policy. There's so much else to do in life besides working out, don't let it become too all-consuming.
Clare