This is a great (and commonly asked) question. You have 2 years from the date you were injured to file a claim for benefits.
If your claim is for an occupational disease, it must be filed within 2 years from the date the doctor tells you the disease is work related, or five years from the date you were last exposed to the work condition causing the disease, whichever is sooner. Note: certain diseases like asbestosis, byssinosis, silicosis and coal workers' pneumoconiosis have different limitation periods.
If, after returning to work, you suffer a disability, you must file a claim within 2 years of the date for which you were last paid compensation under an award. This is known as a "change in condition." Payment only goes back 90 days from the date of filing with the Workers' Compensation Commission.