Yes, i have set like, but it not run as cron time. It is usually delay 1 to 2 minutes, sometimes more than 10 minutes
That is because they aren't cron tasks in the sense that they run at a given time without any other trigger. vB's scheduled tasks only run when someone visits your site. And they run in a given order, so your task won't run until all tasks ahead of it have been completed. This can take hours on some sites. So, all tasks can be delayed.
Yikes! running those scheduled tasks could lead to trouble with your host, if you are on a shared hosting plan you are only allowed 25 process if that, having something like this every minute will definitely make your host shut you down quick.
It might take me some time but there is several posts here -- I think -- on how to use your OS to run cron jobs. I run my vb cron jobs via the OS, but my setup won't help you unfortunately.
Maybe someone else knows where these posts are. I put you on my backlog and will do a bit of research for you later.