Break it down a bit, doghead. What is the threat? The town getting the disease? If, so what is the problem? The ritual itself? If so, the flow is a bit muddied. A race against time, for sure but what is the dynamic player actions that happen to progress things? Waiting for the DM to reveal things is a bit dull. Players discovering things and acting on them is AWESOME!
You'd need to be strong at 'on the fly' stuff but any idea from the players that is clever and creative needs to be rewarded. Resolution is entirely dependent on player action. I've taken to creating the bad guy timeline, giving Him/Her/It/Them a few Assets and then react to player actions. They'll take umbrage at something eventually and fight back.
I've also found that having the Timeline frees me up to act and react to the players actions. I don't spend so much time pre-planning as I do getting ready for the next session. You've got the Timeline and an understanding of the system... keep us posted!