According to this on the CNBC website, quoting the NY Times, you will be able to get the higher bonus in branch until March 12.
http://www.cnbc.com/2017/01/04/jpmor...s-in-half.html:
...Now the bank is cutting the bonus in half. Jan. 12 will be the last day that people can earn it by applying for the card online, though people who apply at a bank branch will still be able to get the bonus until March 12. You need not be a current bank customer to apply at a branch, according to a bank spokeswoman, Ashley E. Dodd, who confirmed the changes...