As I understand it even a small difference in temperature between the surrounding air and the seed (the seed having a lower temperature) in the soil will result in condensation on the seed so allowing it to imbibe . Obviously the higher the RH the more rapidly the seed should imbibe as soil temperature alternates through out the daily cycle. The following may also help

Development of combined imbibition and hydrothermal threshold models to simulate maize (Zea mays) and chickpea (Cicer arietinum) seed germination in variable environments

Finch-Savage et al.,New Phytologist Volume 165, Issue 3, pages 825–838, March 2005