Strange thing, as usual with Grandaddy's synths !
Indeed it sounds like it's speeding up then slowing down. Actually, the first 4 notes (C, C, E, G) are played with a "16th triplets" feel (C - - C E G), then the next C, E, G, C, E sound like a quintuplet. But the top G playing on the next bar comes a bit off, though.
As for the synth itself, no idea, but this particular one here sounds very basic, like a sine wave. There's a forum here where the guys talk about Yamaha (PSS and the like, probably) and Casio (CTK series) :
https://messageboard.tapeop.com/viewtopic.php?t=1929
Excellent album, by the way - and excellent band, of course !