Securities and Exchange Board of India (Sebi) is likely to amend the guidelines on 25% public holding in all listed companies, and come up with a time frame soon for meeting the norm."Sebi is now reviewing the guideline. A time frame will be spelt out for listed companies," a senior Sebi official said today.Though Sebi had issued a circular last fiscal on the minimum public holding a listed company must have, there was no time frame fixed for meeting the norm.Sebi had restricted promoters having more than 55% stake to acquire up to 2% shares every year without taking its permission instead of the previous limit of 5%.