Blisters After IPL/Broad Band Light on Arms?

It can take up to 2 weeks for the coffee grounds to completly lift and flake off.  Make sure you keep an aquaphor type product on and keep the area out of the sun.  You might need an additional treatment in a few weeks at a lower setting to even it out. 

The skin on the body usually takes about 14 days for the coffee-ground colored spots to fall off.  Keep your skin well hydrated with Aquaphor or a lipid-based cream, like CeraVe.  Because you experienced blisters, you may have lighter skin (sometimes called "striping") when the scabs fall off.  This can be resolved with future treatments, ideally done in a pattern perpendicular to the pattern of the stripes to help blend it more evenly. 

The coffee ground color and scabbing will probably peel off in another week.  Keep the areas moist with Aquaphor.  You must avoid sun exposure on the new skin since it will develop brown pigment if exposed to the sun.  If you had blistering, it is possible that you may have lighter areas left but hopefully with time, the color will be even. 

It's good your technician told you to keep the area moist, and I'd recommend you keep doing that. Additionally, you need to keep the burned areas covered and out of the sun, or those areas could potentially burn very badly. Hopefully you won't be left with any hyper or hypo pigmented areas from the treatment, but it's very important to keep the areas moist and covered. The coffee grounding and scabbing will resolve over the next week or so - do not scrub or exfoliate - let it come off on its own. Additionally, please make sure any subsequent treatments are not done with any higher settings, or you most definitely could have bad, permanent scarring and burns.