iRule to disable a pool to new connections

Sure thing, though after thinking about it I've had a slight change of heart. The code below should do what you need:

when RULE_INIT {
    set static::START_OFF_TIME "09:30 AM"
    set static::END_OFF_TIME "10:00 AM"
    set static::DOWN_POOL "local-pool"
    set static::DOWN_MEMBERS [list "10.70.0.1 80" "10.70.0.2 80"]
}
when CLIENT_ACCEPTED {
    set start_off_time [clock scan $static::START_OFF_TIME]
    set end_off_time [clock scan $static::END_OFF_TIME]
    set now [clock seconds]

    if { ( [expr $now > $start_off_time] ) and ( [expr $now < $end_off_time] ) } {
        foreach x $static::DOWN_MEMBERS {
            LB::down pool $static::DOWN_POOL member [lindex $x 0] [lindex $x 1]
        }
    }
}

The idea is that, at the given time period, selected members of the pool are marked down in the CLIENT_ACCEPTED event. This prevents them from being selected in the LB decision. I've added two new static variables:

set static::DOWN_POOL "local-pool"

This is the name of the pool, though you could also derive this with [LB::server pool] in the CLIENT_ACCEPTED event.

set static::DOWN_MEMBERS [list "10.70.0.1 80" "10.70.0.2 80"]

This is a list (IP and port) of each pool member to take down at the given time period. The CLIENT_ACCEPTED event loops through this list, removing these members from pool selection. You could still use the USER_ALERT method, but it becomes a bit more complex as you also have to manage bringing the members back up - an event that wouldn't be triggered until someone made a request.