As mentioned briefly in the introduction (§ 2), XRPS is a pure online submission system, which depends on the performance of the computer links to the XMM SOC as well as the machines running the software. The performance of XRPS, as experienced at the user's institution, is hard to predict. Therefore, it is strongly recommended that proposers try to avoid submitting very late during the AO-1, close to the deadline. Early submission will help to alleviate such problems.