Shade does delay bloom- I've observed it so many times that I can say that unequivically, but sun makes fruit sweet good and plentiful- hence the value of shade that kicks in in Sept or so. So low southern shade is all you can count on to really work well.

Christe:

Soil temperature or shade is only likely to make a few days difference in blooming date. That might make a difference one year in ten.

Robada is a high chill variety. But in your climate that probably won't make all that much difference in bloom date either. Maybe a week or two at most and then only compared to very low chill or very early bloomers. I do think it will bloom with the later types and not the earlier.

I didn't get enough chilling here this year to get a good bloom on any of my several Robada either indoors or out.

I think FN is right. Apricots are extremely unreliable in areas subject to late frost and delaying bloom for a week probably wouldn't solve the problem appreciably.

To answer the original questions in your title: it is certainly not day length that effects bloom time in apricots, but rather the temp of the air and soil. The low-wall idea will probably buy you a few days, as will the full spring shade idea as well. I've experimented with both, and they do work, but only minimally.

I cannot speak directly to apricot, but I think the temps of the twigs is what matters most via air and sun.

I frequently generate a tremendous amount of wood shaving in the shop over winter, Often I will dump them along and in the rows of blueberry plantings....on top of the frozen ground and snow. Those rows will hold the ground frost weeks beyond those that don't get this "treatment" and all still bloom together. (I don't do this in an attempt to delay bloom but just to get the stuff out of my way and on the berries)

I also know folks around here who have tried to mound snow on their plums to delay bloom as well. That treatment seems a bit less effective in holding ground temp as long but they tell me it had no noticeable effect on bloom timing

air temp...from everything i've experienced in my yard, its air temp over everything else...sure, i think root temp has some sway, but day length? Nope..not with apricots..they'd flower in Jan if given enough chill... peaches not much better.

Last March ws teh warmest March on record...+16F for the month..we had 70Fs and 80Fs over a week stretch... i had trees with frost in the ground budding out...peach trees...after seeing that, i came to realize that warm temps are the enemy of the early bloom.