This article outlines the down hold-time support on QFX5K Junos platforms.
set interfaces <> hold-time up <> down <>
When a hold-down timer is configured and the interface goes from up to down, the down hold-time timer is triggered. Every interface transition that occurs during the hold-time is ignored. When the timer expires and the interface state is still down, then the router begins to advertise the interface as being down.
Similarly, when a hold-up timer is configured and an interface goes from down to up, the up hold-time timer is triggered. Every interface transition that occurs during the hold-time is ignored. When the timer expires and the interface state is still up, then the router begins to advertise the interface as being up.
For QFX5K Junos platforms:
The link state changes may not be detected correctly if the hold time down is not 2x linkscan interval or higher. For example, with the default linkscan interval of 500ms, hold-down time below 1sec will not correctly detect the link state changes. Configuring an unsupported hold-down time (less than 3 seconds) can cause brief traffic loss after the link comes up.
https://gnats.juniper.net/web/default/1865593#description_tab