sokolov according to the latest email regarding this project and the current indication on the corresponding website, some (quite a few) of the hospitals have already gathered enough miles to cover all of their staff, so you should only donate to the ones that haven't gathered enough miles yet, even though if (them being big hospitals) they already have even more than 4000 tickets worth of miles!
Edit: They have now also set a cap on the total amount of miles to be collected for all hospitals at 480.000.000 and it will come quite close (7 hours left for 43.000.000). And indeed the hospitals where the "arrow" isn't working all the ones that have reached their respective required amounts.