Alejandro:
- Re your original question.  If your "touch up" operations are done on
plated through holes you should probably be using a lower temperature (600F
to 625F at the highest).  If "touch up" is being done on surface mount
components (either leaded or leadless) you should probably be in the range of
550F to 600F - never higher than 600F.  There are many things that influence
the correct tip temperature for a rework or repair activity.  The type of
solder, type of flux, size and thermal mass of soldering iron tip, thermal
characteristics of the component and pwb will all influence the temperature
that needs to be used.  As the principal writer of the IPC Rework/Repair
Program I still teach rework and repair classes now and then and advocate in
the classroom that students complete soldering rework and repair activities
at temperatures below 600F just to prove to themselves that it is possible.  
- Your question begs the following question:  "Is rework appropriate or
necessary?"  Rework should be conducted only when there is a reliability
impact if the condition is NOT reworked.  Although a reworked solder
connection may be "prettier" on the outside several negative things happen
internally during rework (even when it is done correctly).  The rule of thumb
needs to be, if it doesn't impact reliability, leave it alone (if it ain't
broke, don't fix it).       
- Hope the above helps.  If you need additional information about specific
rework challenges please contact me off line for additional information.  
Jim Moffitt, Moffitt Consulting Service, 317/773-5570