There is nothing in the Red Book standard regarding gaps between songs, only the requirement that there be 2 seconds of silence before the first song.
Don't forget the creative possibilities of varying the gap or eliminating it altogether. A standard technique is to count off a measure at the tempo of the previous song and start the next song on the imaginary downbeat. Or, if two songs are in the same key like all of the Coffee House Band's, run them together and let the second song fade in as the first one's fading out. Such things were novel back when the Moody Blues first did it, back when you had to use razor blades on tape, but nowadays it's a piece o' cake. Still effective, though.