The FA report that all ties must be played by 31st January but add 'unless mutually agreed otherwise', which is happen as well given that only one 4th round tie has been played which has seen Newcastle go through having won at Millwall.
The 4th round tie at home to Cardiff will be played at Turf Moor on Tuesday 20th January, kick off 7 p.m.
The full draw is
ARSENAL or ROYSTON TOWN v CREWE or BOLTON
WEST BROM or NOTTINGHAM FOREST v BURNLEY or CARDIFF
LIVERPOOL or DERBY v BLACKPOOL or BIRMINGHAM
EVERTON or SOUTHAMPTON v LEICESTER or CHESTERFIELD
CHELSEA or HUDDERSFIELD v SWANSEA or DONCASTER
SUNDERLAND or IPSWICH v NEWCASTLE
TOTTENHAM or WOLVES v MANCHESTER UNITED or HULL
MANCHESTER CITY or COVENTRY v MANSFIELD or STOKE