My last 3 runs have all been kicked off with a SARM cycle, and then bridged into a PH/DS. It's a great way to make some gains and at the same time dial in your diet and training and shed some BF with a non-aromatizing and mostly side-effect free (for me anyway) compound. Eating at but especially under maintenance while running a SARM can really help you to cut some BF prior to the PH/DS portion of your run, while at the same time starting the quickened process of developing new muscle tissue. Increasing your calories when bridging into the harder compound can really accelerate tissue growth if macros/diet is in check. My last two SARM kickstart runs were..
LGD - 8/8/812/12 (37 days) stacked with Dermacrine. I gained ~ 10 lbs and had no vivible sides.
Ostarine - 20/20/20/20 (30 days) stacked with Arimisatne (El1minate) and Dermacrine. I gained 5 lbs and had no visible sides.
The longer cycles will make it easier for your body to get used to and keep the added mass. Of course, with longer cycles comes more chance for harder recovery. For me, it has not affected my recovery or the ablility to maintain my gains one bit. With anything, results are user dependent.
If it's your first or second cycle, I would advise picking one compound and finishing a full cycle/PCT before considering stacking and bridging options. If you have run a SARM before and find them to be overly supressive or hard to recover from, I would advise against stacking, unless you are prepared for the drawbacks of 'feeling' overly supressed or having to endure a harder recovery. Again, it all comes down to experience and this is why we experiment with various compounds on their own before we start bridging and stacking.
As far as how long to run a SARM cycle when bridging into a harder compound, it really does depend on how you respond to the SARM itself. I would advise that 30 days should be a minimum consideration. If you can't make gains in 30 days on a SARM (even a slow-kicking one like Ostarine), you may need to re-evaluate your diet/training or maybe your SARM source.
Another thing to consider when bridging is your layout. If you are bridging into a slow-kicking PH/DS/AAS, you will want to start it during the last two weeks of your SARM run. This will allow the harder compound to kick in before the SARM portion ends. My last run bridged from LGD straight into Trest (no overlap) but it was not necessary because Trest is a short-estered and fast-acting compound. If you were bridging into a compound like Halo (which often takes 3+ weeks for full affect), you would be wise to overlap the compounds. Overlapping also allows for the longer bridged run to be bit shorter and thus you will have more time available off-cycle for recovery and maintaining homeostasis.
As always, increasing your chances usually increases your risks. It's all anout risk versus reward in this game; And of course, YMMV. Know yourself, know your body and know your compounds. Feeling confident on cycle with the knowledge that you have covered all of your bases will allow for a better mental response to being on cycle. You can always tell when people are ill-prepared.