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More precisely speaking, to process a submitted GNSS dataset, OPUS-RS needs (1) corresponding GNSS data from at least three CORS and (2) corresponding GNSS satellite orbits. Moreover, OPUS-RS uses CORS data that spans a time interval which extends the time span of the user's data by as much as 26.4 minutes in each direction. OPUS-RS uses this extra span of data to accurately estimate atmospheric parameters that characterize the refraction delays experienced by the user's GNSS data. Now, most CORS data are collected hourly within 30 minutes after the turn of the hour. However, some CORS data are collected only daily within 4 hours after midnight at Greenwich, England. Hence, NGS recommends that users do NOT submit their GNSS data to OPUS-RS until at least 30 minutes after the turn of the first hour which occurs at least 26.4 minutes after the end of his/her observing session. The chances of having GNSS data available from more CORS are improved, if the user submits his/her GNSS data to OPUS-RS at least 4 hours after the first Greenwich midnight following the end of the user's observing session. NGS studies reveal that the accuracy of OPUS-RS results generally improves with the use of data from additional CORS. Hence, OPUS-RS will use data from as many as nine CORS, if these data are available (and if these CORS are within 250 km of the user's data-collection point). Also, the accuracy of OPUS-RS results should be better if this utility is able to use the `postfit' satellite orbits, as opposed to the `predicted' satellite orbits, generated by the IGS. The IGS releases new orbits four times per day at 3:00, 9:00, 15:00, and 21:00 relative to Greenwich time. Moreover, each release contains postfit orbits for up to 3 hours before the release time. Hence, a user never has to wait more than 9 hours (and he/she may only have to wait as little as 3 hours) to have OPUS-RS process his/her GNSS data with postfit orbits. Note that accuracy differences between postfit and predicted IGS orbits continue to shrink as understanding of the underlying physics has improved over the years.