Apply for work permit renewal 6 months before the expiration date of current work permit..

Work permits are good for two years. Unfortunately, renewal applications are currently taking a long time for U.S. Citizenship and Immigration Services (USCIS) to approve – often much longer than the six-month automatic extension that was granted by USCIS. The USCIS site currently shows processing times between 1.5 months and upwards of one year, depending on processing location.
Although the USCIS site says the extensions were implemented “to help prevent gaps in employment authorization and documentation,” for many people the extensions are running out long before work permit renewal processing is completed. This has resulted in people losing their employment.
If an application for renewal is filed before the old permit expires, and the filer has a receipt proving this, then the old work permit is valid for an extra 180 days after the expiration date printed on it.