The applet that tracks your IP SLA objects (I'm guessing you have a tracked object that tracks a list of other objects) should configure another timer applet that counts down the time you want. For example:
event manager applet track-down
event track 3 state down
action 1.0 cli command "enable"
action 2.0 cli command "config t"
action 3.0 cli command "event manager applet countdown"
action 3.1 cli command "event timer countdown time 4500"
action 3.2 cli command "action 1.0 reload"
action 4.0 cli command "end"
!
event manager applet track-up
event track 3 state up
action 1.0 cli command "enable"
action 2.0 cli command "config t"
action 3.0 cli command "no event manager applet countdown"
action 4.0 cli command "end"