In sim switch settings when you choose "on data connection fail" option there is a choice of LCP or ICMP echo method. ICMP lets you select extra configurations like "Health monitor ICMP timeout" and "Attempts before SIM failover"
If it is set up like this, it will check yours connection every second, and if it fails to ping 184.108.40.206 (Google DNS server in this example) once, SIM switch will be initiated. It starts really fast, but will still take some time to connect to Mobile provider which will still take 30 or more seconds for connection to be up again, depending on yours connection and provider. That is the fastest option at this moment.
Just keep in mind that depending on yours connection quality, setting everything to lowest time, and retry options can start SIM card switching when it is not needed, e.g. couple of seconds connection problem, that would not really influence your streaming, could initiate SIM switch and you will loose more time, so you want to test it few times more before applying it for use.