When will the red skin underneath the flaking start to be less red after Halo?

It can take several weeks for laser results to settle. I recommend following up with a cosmetic dermatologist for a formal evaluation and after care recommendations. I recommend skin care with vitamin c, b5 hydrator, silicone based scar gels with growth factors and enzymatic washes with papaya enzyme to give improvement. Sun protection is essential. Lasers work best in combination with other treatments in order to improve the skin's texture and collagen. After Co2, I recommend adding fraxel lasers, microneedling/prp and radiofrequency treatments. 
Best, Dr. Emer
 

The flaking and redness that you are experiencing is normal and no cause for concern.
Because the Halo is a completely customized treatment, depending on the depth and density of the treatment the post treatment healing can vary from person to person.  Generally, the flaking and peeling will resolve in about 4-5 days.  The redness will often become less noticable about in about a week and often be completely resolved in about 2-4 weeks.  How long it takes to settle completely depends, in part, upon your skin type.
During the healing phase it is very important to keep your skin well hydrated with a non reactive soothing cream like the Lexell by Vivier and it is very important to use sun protection with a zinc based sun block. This will help with the redness. Take good care of the new skin that is emerging. You are able to wear a bit of a non-reactive mineral based make-up  (foundation or powder) like Glo minerals or Jane Iredale to help manage the redness.
Most importantly, follow up with your treatment provider so that they can assess your skin and advise you if anything further should be done to help improve your healing and ensure the best results. Our patients have been getting fantastic results with this treatment and I hope that you are equally happy.

On the 2nd or 3rd day after treatment, you will increasingly notice tiny dark spots and bronzed appearance to the treated skin. This is called the MENDS (microscopic epidermal necrotic debris). In individuals with heavily pigmented skin, or in areas where sun damage has produced pigmented lesions, the microscopic wounds, known as MENDS, contain large amounts of melanin. Because there are so many MENDS, they can make the skin look bronzed and small areas appear crusted (do not try to scratch them off). This is part of the healing process where treated tissue is working its way out of your body as new fresh skin is regenerated. During this time, your skin will be very dry and have a sandpaper texture and will begin to flake and peel. If the face is treated, it could take 2-7 days (or longer) for the peeling process to be completed. If the neck, chest or anywhere on the body was treated, this process could take up to 2 weeks (or longer). After the peeling process is complete, your skin will have a rosy, pink glow that will gradually resolve. Makeup can be worn 24 hours after treatment.  We recommend Jane Iredale Powder with an SPF, or ColorScience Sunfortgettable SPF 50 Powder. Hope this helps.