commuting 12 miles one way.
 

how long do u think it will take?

Depends on a lot of factors: traffic, wind, hills, your own personal level of fitness, the bike, etc.

But, you should probably be able to knock it out within an hour from door to door.

I commute 7.5 miles one way.
The Time of Day seems to be the difference.
Depends on Traffic, School Zones, Construction.
28 to 48 minutes

What type of terrain and how good of shape are you in? It could take anywhere between 40 to 90 minutes to ride.

Everything said above. My ride home, using the very same route, takes about 2/3 the time of my ride in because I'm going down the durned hill instead of up. If I do the ride on the weekend, it takes less time than during the week. Riding in full light in the summer is faster than darkness and rain in the winter. In general, traffic and environmental changes can add or subtract as much as 25% to/from my ride times.

Given a relatively flat route with minimal traffic and stopping, and assuming you and your bike are in reasonable shape, you should be able to do a 15 MPH average, so 12 miles would take about 45 min.

Medium long.

I have a lot of hill climbing at stop signs, and I average 12mph on my 20 miles commute. YMMV

I try my hardest to average over 15, but over 50% of my ride is on an MUP with intersections of any kind so I can make up a bunch of time on that stretch. I have a steep hill on my morning ride, that used to make a big difference, but since I started focusing on my hill climbing strength over the past month or two I barely notice it any more.

40-55 minutes. That's what it takes me on my 12 mile commute anyway. Try it on a day off first, or just leave early on the first day.

An hour or less depending on the factors listed above.

I commute 12 miles each way and the amount of time it takes can depend on a lot of factors. How well I slept the night before, headwinds or tailwinds (they can be strong either way), stop lights, slowing for areas where I have to be aware of people opening their door into traffic, personal motivation for maintaining a certain speed...

It can take anywhere from 40 minutes to a little over an hour to get to work. Rides home always take longer but those are for me to enjoy...times be dammmed.

My 11-mile commute takes about 35-45 on the way in and 40-60 on the way home (accounting for downhill vs uphill and the tendancy to have a headwind in the afternoon).
But then, my route is pretty flat and I've got a mostly-empty MUP for 7-8 miles of the trip. YMMV.
40-60 minutes is a good amount of time to budget for.

My commute into work is 12 miles, and the time it take depends on the wind and traffic once I get into town. There is one heck of a hill north of the airport, which I climb on the way in, and several easier ones (about 3) closer to town. There is one main artery into town that I have to cross with no traffic lights. That can be one of the longest waits. Another is a traffic light near our house that is controlled by a magentic sensor in the pavement. That's when you actually want a car in front or behind you. My trip usually takes an hour, give or take about 5 or 10 minutes.

Yeah... an hour. Also factor in changing time.

My commute is 12 miles one way. On average it takes me 42 minutes to get to work and 37 minutes to get home.

1 hour your first 3 times

45 min the rest.

How long will it take?
 

I ride 8 miles and I plan on 40 minutes, so I'd say give yourself an hour

Mine is also 12 miles. I've got a couple of minor hills to deal with, 16 traffic lights and a handful of 4 way stops. Normally takes me right around 47 minutes. Very consistent times. I can be off 2 minutes one way or the other due to the wind.

We all are pretty consistent, mines 8 miles and it's 35 -45 minutes depending on weather, lights, traffic and how much effort I want to put into it ;)

A couple hours or more if it is gnarly single track.
Seriously, some parameters would help. Elevation, # of stop lights\signs, weather, what you are riding, your fitness level, what else you do besides ride, etc.
My 23 mile ride is taking me between an hr and a half and an hr and 45 min. Lately I have been doing quite a few intervals the day before and my legs feel like mush.

My route is 9 miles and I do it in about 45 to 50 minutes fixed gear and 35 to 45 minutes SS. I have hills to deal with too and that's why it takes it a little more on the fixie.

Mine is also on a FG with 800 feet of climbing. Nothing too bad.

That's the distance of my commute too. From 45 to 70 minutes.

I do 12.5 miles but my commute is fairly flat and rural so i don't have to stop for many lights. (i think there's a grand total of 3 i typically have to stop for).
My best time Ever: 32min50sec
Slowest: 1hour 3minutes
Typical day will be 40-45minutes.

Your mileage may vary. I have a 9 mile fairly flat commute and it takes me 70-80 minutes. But I have an old beater bike and its engine is in even worse shape.