Yes. If you hold on to today's writs and don't actually do them today... Then do them after the patch, they have a chance of dropping master writs. Then you can also do tomorrow's.
Source: I did it for PC, and got a master writ from the "yesterday's" writs.
Woooah. Any of the CONTAINERS you saved are useless in terms of master writs.
The day before only works because you don't get the reward container before the patch... You're getting the container after the patch. @MAEK
Think of it this way. There is an old container with model# 2016 currently being given out. As of tomorrow any containers you get are model# 2017. Only 2017 containers can give master writs, and any old model# 2016 containers in your inventory do not convert... So they still do not give master writs.