why isn't this correct?

These two moons orbit Saturn at 139350 and 141700 , respectively.
Consider the two in a race around Saturn: In one Prometheus orbit, how far behind is Pandora (in units of time)?

I did:
Using Newton's version of Kepler's third law, find orbital period of Prometheus.
14.7 hours

Using Newton's version of Kepler's third law, find orbital period of Pandora.
15.1 hours

Find the percent difference in their distances.
1.66%

Find the percent difference in their orbital periods.
2.6%

Consider the two in a race around Saturn: In one Prometheus orbit, how far behind is Pandora (in units of time)?
0.4 hours.....but it's not correct? AGH!