Hi Teet,
Is there any possibility to lower that time?
You could try, but I think you risk errant failover events if it's lower.
And secondly, I'm using interface failsafe
HA groups should provide faster failover and more intelligence than VLAN failsafe:
http://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/tmos_management_guide_10_1/tmos_high_avail.html1026652
One of the benefits of configuring an HA group is a feature known as fast failover. When you configure the HA group, the process of one BIG-IP unit failing over to the other based on HA scores is noticeably faster than if failover occurs due to a hardware or daemon failure.
Aaron