u are casting in the wrong order if you are using meteor storm and flame burst AFTER the eruption.
Assuming you do not have a staff of enchanting.
Assuming you have a 15 Water
Assuming you are not using an item which makes your spells cast faster
Your Mist Form lasts 20 seconds.
Cast in this order after Mist Form. On the left I note the approximate time the spell STARTS casting - you cast as fast as you can, this is when it will really begin based on the numbers:
0s - Lava Font
~2.75s - Firestorm
~7.5s - Meteor Shower
~13.25s - Eruption
~16.25s Eruption starts
~17 - Lava Font
~19.75 - if you brought a 4th fire spell, now's a good time to cast it--I use Phoenix for ~200 dmg.
20 - Mist Form ends

~21.25s Blindness starts
<cast Lava Font only in this period and keep an eye on your E and your Mist Form and make sure you have 10E available the instant Mist Form is ready and make sure you are not busy casting something else at this time. I usually am low on E and so just hit the spacebar to attack with my staff while waiting on the meter.
30s - Mist Form
Have fun.
I don't know how long the blindness from Eruption lasts. I am thinking it lasts 8 seconds or so as I usually get banged on for the last 1-2 seconds before I get Mist Form back up. Plus without an Enchanting staff, your mist form will end before blindness kicks in for another 1.25 seconds of pain. I can see how it could be ugly. At least you'll get 8 seconds of healing before the blindness ends.
You can improve your odds if you have the collectors fire-staff and hope fire storm or meteor shower goes off faster. Or get an enchanting wrapping for your staff to extend Mist Form to ~23 seconds.
And yes I have the same problem: Once I get 8 or so griffons chasing me I have to stop and start the battle b/c they dmg me faster than I can heal while luring them and even then it is always a *very* near thing to get Mist Form up before I die. I usually mis-time it 1 in 4 runs and die. I'm learning to use bushes as blockers while running to get some distance between me and the griffons.