I would think a chess clock doesn't really work that well for this game, since there is so much interactivity. In WH40K and Warmahordes, it works quite well because, other than saving throws, there is not much the opponent can do while it is your turn. This game has enchantment revealing, using counter-attacks, deciding where to teleport trap someone, e.t.c that will take time from your opponents turn its going to be really difficult to time who's time it really is sometime.
The way I play it now is a 90 min total game time, the one with the least amount of remaining health at the end loses. This should of course give a "modified" win and should be awarded slightly less tournament points than actually killing the opponent. If the turteling priestess wants to win the entire tournament, she would probably have to get a real win at some point. And this would make the maximum turtleing strategy very much a non-competitive strategy. Besides, anyone can put a Deathlock in their spellbook (and probably should in a tournament).
We time the planning phase like this: as soon as one player is done, he/she turns a 30s hourglass, and that is how long time the other player has left to decide.