Generally, the more serious and long lasting the injuries, the longer the claim may take to resolve your personal injury claim. There are exceptions to this, of course, but the general rule is that insurance companies are more likely to push back and deny or devalue a personal injury claim, especially in situations where the victim's damages are significant.
The exact length of time that it takes for a personal injury claim to be resolved is primarily dependent on the length of your medical recovery, or how long it takes you to reach a maximum level of physical improvement.
When you ultimately decide to settle your claim with the insurance company, you want to be sure you have accounted for all of your damages, past and future. You cannot re-open a personal injury claim once it has been settled, so it's extremely important that you reach the maximum level of improvement before you even consider settling the claim.
With many types of injuries, it may take months or years before you know a firm prognosis and how much future treatment may be necessary. It will be in your best interests to wait to negotiate a possible settlement until you have recovered from your injuries and no longer require ongoing treatment.
It is important to wait to settle your claim until you are reasonably certain of how much your past and future losses will be. If your medical providers expect that you will require future medical care or treatment, then that treatment should be accounted for in any settlement discussions with the insurance company.
As confusing and frustrating as the personal injury legal process is, the last thing you want is to settle your injury claim and then discover that you will require additional treatment or care. If you settle your claim before you fully understand the long-term implications of your injuries, you could be left to pay for that on your own.