I hope someone can answer…
At what point should I increase intensity in a training block if workouts feel too easy?
Is it advisable or should I just let my body adapt to the increasing stress for the full 6 weeks?
Can I treat SSBLV 1 and 2 as 3 4 weeks blocks instead of 2 six weeks blocks. If so how can it be adapted?
Thanks.
You are free to adjust FTP (up or down) at any point you think it has changed. There are FTP tests in each plan, but if you feel a change is necessary, go ahead and do it. Keep in mind the general progression that each week in a plan gets a bit more difficult, so keep that in mind but adjust as needed.
You can also alter the work/recovery week structure. I wrote a post covering two possible options.
Thanks @mcneese.chad this is exactly what I was looking for.
As a follow-up question… The weather is still nice here and I still want to ride outside… I plan on adding a 2:30 to 4:00 endurance ride on top of the low volume SSB plan. Though I don’t know if i’ll be able to handle that volume down the road.
I know you guys tend to lean on the conservative side. I ask because I don’t know what to expect at all. The only TR plan I followed diligently was TBLV to which I added some zwift ride and races once a week. And it went well.
I know you can’t tell me if I will be able to handle it. But some pointers on how I should go about testing it would be appreciated.
For clarity, I am not Coach Chad Timmerman. I am just a regular guy and active forum member, but I follow the real TR crew and their typical advice closely.
For your additional volume question, I think you can add more work. The basic suggestion would be to start with the shorter ones (2:30 per your comment) and see how you react and recover. Add more in small steps each week if you are handling it well. Maybe another 15-30 minutes each week up to your desired cap (4:00).
Listen to your body during the week’s workouts and as you move from week to week. Be willing to adjust as needed if you experience issues that are above and beyond the desired stress. Knowing that is not exact and takes some experimentation and reflection. This is all trial, error, evaluation, and hopefully… learning 
In addition to what @mcneese.chad said, a clear sign is if your RPE is much easier than what you would expect for that training zone or it doesn’t coincide with the workout text. For instance, if threshold intervals feels like sweet spot. This will require some experience in structured training to realize this though. Regarding the workout text, if during the workout the text is telling you to “hang in there” but you’re not really struggling, then it’s time to up the intensity. If you find that you’re always upping the intensity of workouts, then it’s time to manually adjust your FTP up.
However, keep in mind that recovery rides are supposed to feel easy. Make sure you’re not upping the intensity on days that are supposed to be easy. Lastly, SSB 1 starts off quite easy and gentle, but will ramp up as the weeks progress. So if you up intensity or your FTP, be conservative.
As an update I did Monitor 2 days ago and I’m scheduled for Antelope today. Monitor felt easier than Mount Field. I finished intervals at 83%, 83%, 83%, 86%, 86% , 87% of max hr defined as the highest HR from ramp test at 182. And completed the work out at higher cadence than Mount Field at 92 RPM. The workout didn’t feel challenging at any point. And I was on an off day with very little sleep.
Certainly, not “challenging but manageable” neither physically or mentally.
I just don’t know if I’m being impatient, or if my FTP is really set too low.
When workouts start getting a bit too easy I just knock the intensity up 2-5%. Things I personally look for are threshold workouts should be uncomfortable, and over under workouts should have the burning lactic acid feeling on the unders. I took some time off recently for the birth of my son, and I think my fitness is coming back faster than expected, so Im making good use of that intensity slider.