RepricerExpress will regularly send batches to Amazon with your new prices, so that Repricing can take place.
You can check these uploads directly on Seller Central under Inventory > Add Products via Upload. You should then see a tab called 'Monitor Upload Status'.
You will then be able to see the Status of each upload. If you see many 'In Progress' this would generally mean that Amazon is having backlog on their end processing uploads, which means that your Repricing might be delayed.