How long does it take to refuel a Cessna Citation X+?
Basically fuelling time depends on how fast the hydrant or fuel truck can deliver fuel.
This comes from SmartCockpit:

The  Citation  X  fuel  system  is  comprised  of  the  storage,
distribution,  refueling/defueling,and  indicating  systems.    The
storage  system  is  made  up  of  a  set  of  integral  tanks  in
each wing,  and  a  center  wing  tank  which  includes  a  forward
fairing  fuel  tank.    Each  wing  tank  has  a hopper  tank  which
is  integral  to  it.    The  two  wing  tanks  incorporate  check
valves  and  baffles allowing  each  wing  tank  complex  to  function
as  a  single  tank.    Other  integral  components  of the  storage
system  are  the  gravity  fuel  fillers,  drain  valves,  flapper
check  valves,  vent  system                      components,
positive/negative   pressure   relief   valves   and   all   of   the
associated   system plumbing.    Transfer  capability  is
incorporated  enabling  all  usable  fuel  to  be  available  to
either engine.Each  wing  tank  holds  a  total  of  521  gallons
(3518  Lbs.)  of  fuel,  which  includes  the  hopper tank.    The
center  wing  tank  holds  888  gallons  (5594  Lbs.),  207  (1397
Lbs.)  of  which  are contained  in  the  forward  fairing  tank.
Total  fuel  capacity  of  the  airplane  fuel  system  is
1927 gallons; at 6.75 pounds per gallon the available fuel weight is
13,031 pounds.
SINGLE-POINT REFUELING DEFUELING SYSTEM
The  single-point  refueling  system  is  provided  to  enable  the
airplane  to  be  refueled  or    de-fueled  more  safely  and
conveniently  by  connecting  to  one  port,  which  is  not  open  to
the atmosphere.      Advantages   of   a   single-point   refueling
and   defueling   include   minimized refuel/defuel   time,   reduced
possibilities   of   fuel   contamination,   reduced   static
electricity hazard, less airplane skin damage, and there is no
personnel contact with the fuel.The  refueling/defueling  system  is
independent  of  the  airplane  system.    It  is  designed  for
refueling  with  a  truck  or  refueling  hydrant  (pit)  having
single  point  provisions.    The  major components  of  the  system
include  the  refueling/defueling  adapter  (receptacle),  the
precheck control  panel,  refuel  shutoff  valves,  the  pilot
(precheck)  valves,  defuel  valves,  a  sequencing valve,   manual
defuel   select   shutoff   valves,   internal   drain   valves   and
associated   system plumbing.Single-point  refueling  is  accomplished
by  connecting  the  refueling  truck  or  refueling  pit equipment
to  the  airplane  at  the  single-point  refuel/defuel  adapter  on
the  right  side  of  the fuselage just forward of the wing leading
edge.