Hi roxborough & all, from my experience growth is dependent on temperature, by this I mean when temps., remains low then the tubers will remain dormant.
If the temps., are raised to minimum 10 oC with max temp., 15 oC + then the tubers will initiate growth, untill green foliage appears the presence of fertilizer will have minimal effect.
The use of a temperature dependent fertilizer (here in Australia we use 6month Osmocote exact) which as the temps., rise the fertilizer starts to be released, hence starts feeding the shooting tuber when they have green leaves.
I tend not to feed most tubers, until they have shown green shoots (this is when I use 6month Osmocote exact). Once the foliage has developed sufficiently I use stronger fertilizers.
Dahlias can be kept in flower during winter, by adding lights in the middle of the night for approx., one hour, as this sends false signals to the plant that the season is summer instead of winter. This is the reverse process to flowering poinsettia.

Am still curious how the US snow storms are going? as I do not watch TV often, hence tend to miss the news which would show images & give reports on the extent & severity?

From what I have seen, it looks very stressful (if not terrifying?) to say the least for many people. The forum is very quiet gives me the impression people are occupied else where? would like a quick summery if any one has the energy & inclination thank you allan

You should treat the plants as though they were growing in a greenhouse. If they are growing and it is warm enough to get them to grow, you should feed them with 20-20-20 soluble green house fertilizer after they have sprouted. It should be used at half the normal rate and done a couple of times a week. Sun and heat plus water and fertilizer is what grows plants. If there is enough light and it is warm enough, the addition of the fertilizer will give them a real kick start. Here in my garden, I have noticed that the earliest blooms come from the cuttings I take in early Spring and grow to about 12 to 18 inches tall before planting in the garden. I do not bother to to replant them into larger pots and they are in 2.5 inch pots. They are root bound and somewhat tall but have stiff stalks because of the fertilizer. Since they have such a developed root system, they can grow very quickly when planted. If I plant a tuber in the ground on the same day I plant the root bound cutting, the cutting blooms a full month before the tuber. At a trial garden for dahlias, they accept both rooted cuttings and tubers to trial. They plant the rooted cutting 3 weeks after they plant the tubers and the cuttings still bloom well before the tuber grown plants.