Slow to start, happy now

So, a few days ago, I started my first batch of cider. Started out as 4.5 gallons of Wal-Mart hard cider with ascorbic acid added, threw in 3 cans of Kroger brand apple juice concentrate and White Labs English Cider Yeast (WLP775 I believe). Initial specific gravity was 1.058. I pitched the yeast on Sunday, 3/1, but after 48 hours, saw very little, if any activity.

Finally, I bought a strip thermometer for my Ale Pail and realized that it was at 55 degrees! Last night, I moved the batch to the furnace room, and it's now happily fermenting away, with 1-2 bubbles per second.

Anyone have any thoughts on when I should rack to my secondary? Or is it just based on activity and SG readings?

The only accurate way to tell when your cider is finished fermenting is taking a gravity sample.

I want to wait until fermentation has completely finished before I rack to the secondary? I figured I'd want at least a little fermentation still going on to produce enough CO2 to fill the headspace, is that not the case?

I secondary when it gets down to abour 1.010-1.020 but often miss this so just try for that range.