The only 'Official' information we get is from Forum Staff posting, and telling us that 'this is from the developers', or (now) if something is posted o the Official Wiki (as opposed to the player run wiki). Very little of this sort of data gets there.
If I had to guess what they probably did, it would be one of 3 options, the first is that they didn't really think about it, and the positioning is somewhat random, hopefully keeping the choice through the day. This is quite possible. The second is that they thought about it and the two guilds keep their relative order (who ever was ahead, stays ahead). The last possibility (and if this is what happens, it would be confirmable when it happens) is that they just declare a tie (and for the top ranks share the same bonus).
Except for the last case, which leaves a fairly obvious sign when it happens, the only way to figure it out is to take careful notes and see what happens when it happens. Since one of the options is randomness, you would want to get a number of occurrences with the data behind it to get a reasonably sure answer.