Prosecutors usually move cases along more slowly when defendants are not in custody. As a result, witnesses can disappear and cases can get stale, so that bailed-out defendants often wind up with better deals. As defense attorneys like to say, "Justice delayed is justice."
Yes! In California, bonds can be posted twenty-four hours a day, seven days per week. But whether you can bail someone out of jail at any time depends on their situation. When someone is arrested, they have a first appearance soon after.