It's probably important to first clarify what is meant by nonablative fractional laser. That term is often misused. Ablation means to remove the surface with vaporization. Most fractional lasers are not truly nonablative. For example, fractional CO2 such as ActiveFX, DeepFX, Repair, CORE, Mixto, all cause an injury to the skin and are not nonablative. Other fractional lasers such as the Restore, Refine, Pearl, Profractional also cause an injury to the skin but they are often called "nonablative" resurfacing.
So if you're having a fractional laser that causes a thermal injury to the skin, then It's better to wait until your face is properly healed. I usually advise my patients to wait at least a month before having an IPL treatment after fractional resurfacing.
There can be residual redness or discolorations after fractional CO2 that can improve or completely resolve with time. As with any resurfacing procedure that causes a thermal injury, a patient can develop prolonged redness or discolorations that may not resolve on their own without assistance. Performing IPL after fractional laser can help speed up the healing time if it's done properly. This should only be done by an experienced physician who understands how and when to perform IPL after resurfacing. It should not be done at the normal settings because the patient's skin is more sensitive after resurfacing, has more density of oxyhemoglobin (causes red) and melanin (causes brown) which absorbs more of the IPL energy. If the IPL treatment is performed incorrectly (ie: too high fluence or energy, incorrect settings, etc.) the redness and discolorations can actually worsen, and the patient can develop worsening pigmentation known as post-inflammatory hyperpigmentation.
There are noninvasive lasers that work better than IPL at clearing redness and pigment because they are more specific for oxyhemoglobin and melanin and penetrate deeper, therefore are more effective at clearing the targeted lesions. These include KTP, Nd:YAG, and pulsed dye lasers. It's also possible to combine IPL with different lasers to achieve a better effect. Once again, these procedures should only be performed by a highly skilled physician who has a lot of experience doing resurfacing and understands the ins and outs of when and how to utilize different lasers or IPL after fractional laser in order to enhance the results or speed up healing.