Many of the first Christians were Jewish, and when it was still considered a "form" of Judaism they would go to Temple services on Saturday and meet for Christian services on Sunday. Over time the need to sharpen the differences arose and the day of worship was indeed a marked difference. Christ arose on Sunday. Linking this to appeasement of pagans doesn't do justice, unless justice is considered anything that tars the Catholic Church.
SD
There is no proof that Jesus rose on Sunday, in fact he rose between the legal sunset and the Jewish sunset, which would make his resurrection time up to the person who had a personal reason for wanting either one.
In all accounts of his resurrection, it states that at sunrise he has risen, which is a past tense term which could mean from one minute ago as far as day's ago.