Question about Resource Regeneration

[Sai]

Do resource fields regenerate at a static preset time or at a interval (depending on when the server was put online after a maint)?

Do all resource fields regenerate at the same time of each other or can they be out of sync with others?
(I remember high resource fields were set to 4 hours or something but I cannot reconfirm as this forum has a crappy search function that doesnt allow you to search common words or specific short words correctly IE "4 hours"..)

[GMNyx]

resource spawn rate is based on how many players are online