I wouldn't fertilize til they're in the ground or final planting space, but it sounds like you could water more than sparsely at their height.

Just out of curiosity, what led you to the decision not to pinch?

Thanks Poochella.I did fertilize them with a transplanting fertilizer by MG.I made it double dilute.I am not watering much at all.The potting mix is moisture control and that keeps it nicely at the barely damp stage.The starts(not sure of proper techie term) are between 6-15 inches tall.I am taking them outside daily to harden off.Lows are still in the 40's around here till later this week.I hope to plant them next week.
The pinching was a case of not being sure of what to do,how to do,and when to do so I did nothing!I checked the Colorado Dahlia society site but really did not "get it".It is my first time with Dahlias and I am very excited.I really want to do the right thing.

Oh yes, the moisture control soil would keep the roots more damp, so good idea on the lightly watering. A transplant solution when going from flat or pot to garden really helps prevent shock.

Not too late to pinch at all. The ADS site about topping also confounds me a bit with all the counting and such. There's no time here to count leaves on many plants so when they are 12-18" tall with 'several' sets of leaves I just snap off the central tip as I go down rows or walk by. Best done in the evening or early morning when the plants are more rigid. Sometimes you'll need to unfurl the top leaves to expose the uppermost center growth. If they're too small to snap confidently, let them grow a few more days.

Mid Island dahlia site has a very good photo of leaving the new growth at the leaf junction unharmed when you top/pinch. Aside from knocking down the whole plant, they're about the only thing you can mess up when topping. It's easy and very worthwhile.

Here is a link that might be useful: Mid Island Dahlia Learning Center