Your eBay products are regularly repriced by RepricerExpress. The frequency will depend on the type of eBay rules you are using.
RepricerExpress will check your eBay competition throughout the day and apply price changes where necessary. You'll find that prices change less often on eBay than Amazon.
Please remember to only use a competition rule if the majority of your products are on eBay's catalogue or if you have listed them on eBay with a UPC/EAN/ISBN and that your competitors have listed with the same UPC/EAN/ISBN.
RepricerExpress will check and upload a new price to eBay every 10 minutes if there has been a change.