How do you identify chords quickly?
Learn to recognize intervals between notes quickly. For example, notes that skip a line or space are a third apart. Notes that skip seven are an octave apart. When reading a chord quickly, read the root/lowest note and then the intervals above it and place them in the key.
How long does it take to learn to read sheet music?
If you are a complete beginner, it may take 1.5 to 2 years before you feel like you are really sight reading. Here's a general rule: the difficulty of the music you are able to sight read well will always be about two levels below the difficulty of the repertoire you practice for recitals and such.