In all honesty, I'd recommend leaving on Wednesday night or Thursday morning, if you can. Any time after 4pm on Thursday just gets too jammed, no matter which road you take. San Bernardino can be even more complex as some families from the North are travelling to their vacation homes in Grigioni and caravans are no fun on that road! Safe travels!
p.s. and if you are forced to go on Thu/Fri, the best thing is to leave at 5am on Friday and travel via the Gotthard. You can also download the TCS app (it's free) to track traffic.
How about going over/under the Simplon? That brings you close to Ascona and Lake Maggiore. You can use the car/train at Kandersteg to Goppenstein, then from Brig to Iselle di Trasquera.
In my experience over many yrs it is always abit random.... good to plan but seems that traffic over the Gotthard has a life of its own... We left last yr on a Sunday morning in July at 8 am from Zurich and had ZERO waiting time, I mean literally did not even slow down.
Then sometimes we try to plan it supercarefully and get in a 6 km queue
So just go with it, plan for the wait and do not get stressed
the peaks are southbound from Thursday lunchtime and from Saturday afternoon northbound until Tuesday.
it really used to be Friday afternoon through Saturday morning and just Sunday that were bad but there is so much traffic going through now that it clogs up.
there are lots of non-local vehicles in the area right now and I would expect a trip south to be progressively busier through this week.
there also should be no roadworks or tunnel work this week and next - they did that last week as far as I could see.
IMO PaddyG's suggestion is very good, especially if you are heading south of Langensee. There are also direct car-trains from Kandersteg to Iselle (Google "BLS Autozüge").
If you are driving southbound on A2, take the Bellinzona Sud exit and follow signs to Luino and enter Italy at Dirinell/Zenna border crossing (much less congested than the A2-A9 Brogeda / [Ponte] Chiasso border crossing and the Lainate jct.
Weekends like Easter are known to be worse......end of April should be better, but alot of people will be doing a 'bridge' holiday given May 1st on a thursday
to be honest, it seems to get into October nowadays.....
but as changeover day is usually Saturday, weekends see lots of German, Dutch, Belgian and more cars travelling down through the tunnels and into Ticino.
Strangely, this week, we seem to be full of Germans and Vaudoise.