The period now commences 10 December and ends 17 January.
The bid, worth SEK 2.8bn ($311m), was made public following approval and registration by the Swedish Financial Supervisory Authority, the Finansinspektionen.
William Hill has agreed to buy 2.3 million shares, approximately 5% of all outstanding shares in MRG at a price per share of SEK 69 in cash.
The settlement will begin as soon as William Hill announces the conditions for the offer have been satisfied or when William Hill has otherwise resolved to complete the offer.
Assuming the announcement is made no later than 21 January, the settlement is expected to commence four days later.
The offer document and acceptance form are available on the Danske Bank and William Hill websites.
