Problems with Field Blend#2

Well, Field Blend #2 is what is in the oven, but I am not sure the problems started with this loaf.  I have had similar problems the last couple of bakes using my starter, first with another Field Blend #2, and then with an Overnight Blonde.  What I think is happening is that my dough is overproofing.  The starter is very active.  I built the levain for this bake in three stages, and each stage doubled in less than 3 hours, when the instructions I was following suggested it would take four hours.  Then, when I mixed the final dough, in the recipe it says the bulk fermentation will take 5 hours to rise 2.5x.  Mine took about 3 hours to get to that stage.  Then it was shaped and put into the fridge overnight for 12 hours.  When I took it out this morning, it was definitely overproofed.  I am baking it anyways, but think it's going to come out the same pancake it went into the oven.  

Should I be using less starter?  Or do I need to just adjust the recipe timing so that it is not in the fridge for so long?  Field Blend calls for a little instant yeast.  should I just leave that out?  I should mention that I live in Central Oregon at 3500 feet elevation, and it has been pretty cold here.  My kitchen tends to be one of the cooler places in the house, so I am surprised that things are rising ahead of schedule.  My starter is 100% hydration, and is about 2 months old.  It is kept in the fridge and refreshed once a week starting two days before I bake.  The first three or four weeks, my recipes went exactly on the schedule in FWSY's recipes, with wonderful results.  The last three weeks, things have not been so successful, always on the too fast schedule.

Any insights would be appreciated!

Kasia