It's 1:1 that is usually fed in spring. Sugar : water 2:1 is usually for autumn feeding. 1:1 is more useful for spring build up because it saves water foraging and allows wider activity within the hive even in poorer weather. As for when, what is the weather like with you? Here it was -2'c again over night with a thick frost, having rained most of the w/e and not climbed above 8'C. Short of giving pollen patties next w/e (on top of frames) with a crown board and fondant above the feeding hole in case they need it mine wont see 1:1 until late March April at this rate. Too much 1:1 feed will simply get laid down in the space you want for laying so not too much, it is a 'stimulant' / 'maintainer' at this time of year, not a 'primary feed' perhaps 0.5 ltr / week for a typical full BB colony.