"just now" would be "an-drasta" I don't know if there is really much difference on the Gaelic side but in English there is a slight difference between "now" and "just now". "Now" implies this very moment, while "just now" usually implies that something just happened. Think of it as the difference between, "A bird flew by just now" and "a bird is flying by now." If anyone can explain the difference on the Gaelic side, I'd appreciate it.
It's EXACTLY the opposite : "JUST NOW" implies this-very-moment, and NOW is implying that something is happening "around now" - your examples are good though : "A bird flew by just now" implies this-very-moment (an-dràsda) and "a bird is flying by now" means that is happenening "around now" (a-nis) ... but for the GAELIC difference - we will have to wait for a MOD - tapadh leat !