You should apply the moment you become a nonprofit organization. However, 501 3 c organizations need to be incorporated. First you should become incorporated in State the nonprofit organization is based. Once this has been done you can immediately apply for 501(c) (3) status.
You might want to back date your 501 3 c organizations newly acquired tax exemption to the date of your incorporation. To do so you’ll need to obtain and file IRS form 1023. Please note this can only be done up to and within twenty seven months from the date of the organization’s incorporation. Should you file IRS form 1023 after 27 months, your tax exemption will only begin from the date the application was made.
However, it is possible to request an extension of the deadline. You can do this by including with you IRS form 1023 a statement outlining the reasons why you failed to complete the application process within the twenty seven month time frame after the organization’s incorporation. You can find certain permissible reasons on the IRS form 1023 guidelines and instructions. If you are having difficulties in filing for 501(c)(3) status it might be both necessary and prudent to first speak to your accountant for advice.