would this be overwatering?
 

First off I do container gardening; as a result the soil dries out much quicker then if you were growing stuff in the ground (like in a plot).

2nd the soil mixture I use isn't actually dirt; using dirt that you'd use in a plot won't work with container gardening (learned this the hard way, from past experience). It typically tends to absorb the water faster.

"Soil" mixture I use is a combination of vermiculite, sphagnum peat moss, lime (dolomitic), and fine pine bark mulch.

I generally water in the evening, between 6:00-8:00 p.m. The soil has completely dried by the time the hot weather arrives in the afternoon.

As a result, if I were to water in both early evening and the next morning, would this be overwatering? That is to say, if I were to water twice in one day, once in the evening, once in the morning would this be overwatering?

If the temps are hot enough then yes its ok. Just because the soil looks dry on top doesn't mean the middle and bottom of the container are dry too. Your plants will generally tell you when they need watering especially in containers. Say if they look slightly wilty or the leaves start to curl and brown at the tips can be signs they need more frequent watering. Also another thing to consider is your soil structure. Peat and vermiculite tend t be very water retentive ingredients.Bark fines not so much. I use bark fines as a main ingredient in my container soils. Just something to consider, good luck and welcome to TV.

Damon