I have a couple of ways of going from '0-100' instantly as you put it.
When playing legato you can practice using a halfspeed/fullspeed system.
What this involves is setting up the metronome to a speed that enables you to play the exercise slowly, and at full speed in the same tempo.
Foe example:
Your top
comfortable speed for triplet 16ths may be 110bpm
So maybe set the metronome to 105 to be safe.
Practice 8th notes triplets for several beats then pop out the run in 16th triplets to complete the bar.
Good patterns:
beats 1 2 3 = 8th
beat 4= 16th
beats 1 2= 8th
beats 3 4 = 16th
beats 1 3 = 8th
beats 2 4 = 16th
Aim for evenness in the rhythm and cleanness in the articulation.
Use this for all rhythmic groupings.
Make your own versions up.
This exercise works great when PICKING the notes too - in fact I think it's even more useful for alternate picking practice.
Now, when it comes to alternate picking '0-100', the above exercise works great, but when trying to literally go from nothing to suddenly picking fast you need another approach.
I have found that just before a fast picking run it helps to do some 'ghost strokes' (as I call them) where you pretend to strike the strings but don't.
It's a little bit like revving the engine with the clutch depressed, then engaging the clutch and getting a bit of wheel spin before speeding away. (maybe this is a bad analogy)
Maybe another way to think of it is like steping onto a treadmill that is already going at running pace - you would need to do some 'air running' before your feet hit the conveyor belt otherwise you would hit the deck pretty quick!
For example
If I need to pop out some semiquavers from nowhere, just before the run I'll do some ghost downstrokes at the speed they will occur in the run.
So if I have 16ths at 180bpm coming up maybe I'll do some ghost down stroke 8ths in this tempo to prepare.
I find this really loosens me up and cleans up my playing.
This approach will only work if the music has space for you to do it, which normally it will.
Otherwise the problem of 0-100 is something that is always going to be difficult - the main thing to do is practice with the metronome a lot, and gradually increase you speed limit!
I also think it's acceptable to not pick every single note in runs like this.
You may be able to hammer the second note in the run then pick the rest.
There are many options
