Ok, you are right. The provision is actually in Sec 35(4) and specifically in the proviso. But, like you said, Chartered Accountants (CA) are not covered under the act.
(4) Notwithstanding anything contained in this section, every employee, irrespective of his period of employment, shall be entitled to additional holidays on the 26th January, 1st May, 15th August, and 2nd October every year. For holidays on these days, he shall be paid wages at a rate equivalent to the daily average of his wages (excluding overtime) that he earns during the month in which such compulsory holiday falls. Provided that the employer may require any employee to work in the establishment on all or any of these days, subject to the conditions that for such work the employee shall be paid double the amount of the daily average wages and also leave on any other day in lieu of the compulsory holiday.
I had picked this information from nitekrawler.wordpress.com [https://nitekrawler.wordpress.com/2008/10/13/labour-laws-bombay-shop-establishment-act-1948/]
Bare Reading of sections of the Bombay Shops and Establishment Act relevant to working hours does not mention anything about double payment. CA firms are not a shop under the Bombay Shops and Establishment Act as per the judgment in the case filed by AF Fergusson and six others, leading CA firm.