How to approach scheduled rules to real deathline?
Rule scheduler works with CRON only so you have to run CRON frequently, but you can use Elysia Cron module, where you can specify different schedule for different hook_cron(), so if you want your rules scheduler to run frequently then configure rules_scheduler_cron() to run say every five minutes and  configure other hook_cron() to run every two hours.

In that way you run reduce the load.