You can use .delay()
with a function to do this:
d3.select(".line")
.attr("stroke-dasharray", totalLength + " " + totalLength)
.attr("stroke-dashoffset", totalLength)
.transition()
.delay(function(d, i) { return i * 1000; })
.duration(1000)
.ease("linear")
.attr("stroke-dashoffset", 0)
.each("end", function() {
d3.select(".label")
.transition()
.style("opacity", 1);
});