A minimum of 15750 standing is required for R30, with a 2250 average standing per mission this would be about 7 missions + some overhead. I would estimate this is achievable within 1 1/2 to 2 hours. That is quite short. But while i wouldnt say that its enough time to gather experience for new players, i recently saw some people repeatedly joining with fresh characters after (i assume) they were banned by a gm in asylum. So the R30 condition would definitely help out with that issue.
If you plan to raise the rank requirement, please keep in mind that fight club is needed to complete the tutorial and thats ideally what new players should do.