ssb: Calculate HEAD time and readback times

Author: rye

scripts/should-skip-build

@@ -127,6 +127,8 @@ def git_log_between(source, target)
 end
 
 def anything_changed_yesterday?
+	head_time = Commit.HEAD.time
+	readback_time = head_time - 26.hours
   yesterdays_changes = changes_after('26 hours ago').unique_lines
 
   yesterdays_changes.count > 0