Xero impose a daily rate limit on all Add-On partners for their service, this rate is non-negotiable for any third party add-on. When we run a client’s first backup, it is a full backup of everything held in Xero that we have access to via the Xero API. Most first full backups can take a couple of days or sometimes a few weeks to retrieve the first full set of data. Thereafter, the daily backups are purely data changes made in the last 24hrs and complete in less than a couple of minutes. This is due to the amount of data specific to each Xero organisation as some can have lots of data and others very little - maybe just starting up.
To summarise, the API exceeding the daily limit is a normal function of any app that interfaces to Xero, it is not a fault, only a stand down period until the next day begins and the backup then picks up where it left off until it has completed its task. This is not an error of Control-C, nor Xero, just a state.