Fingerboard and Frets:

On fret-less instruments the bow in the fingerboard must be accurate, to prevent the strings from buzzing off of it, the accuracy of pitch is controlled by its player.  On fretted instruments the frets have to follow the same bow precisely, as well as have to be spaced properly to form properly pitched notes.  In any case, the bow in the fingerboard is the most critical component in the playability of the instrument, and because of the length of the neck, it is also the hardest to achieve.

For reference, a deviation of 0.00001" (one hundred-thousandth of an inch) is enough to cause a buzz at the physically lowest possible action.  That is mathematically based on the space a vibrating string occupies, and does not take the materials, and their physical properties into account.

In the end, there is no such thing as a perfect fret job, but you are much more likely to get a better one from a competent and caring luthier with basic hand tools, than on a brand new instrument made in most factory's, as there is no machine yet, that can level frets right.  I consider myself a competent and caring luthier, I have great tools, and know how to use them properly, with excellent control and finesse.

The time needed for leveling a fret-less fingerboard or the frets of a fretted one is around 1 1/2 hour and can take as long as 3 hours.  Installing all new frets takes at least 3 hours and can take as long as 7 hours for necks with binding, and for lacquered fingerboards add an additional hour or two.

Bridges and tail pieces:

The bridge of an instrument is the main point where the vibrations of the strings are transferred to the body or soundboard of an instrument, and there is a great amount of wanted string pressure in a few different directions, that can cause trouble.  For the most part setup can take care of small problems, but if wear or damage is beyond the point of adjustment, parts of the bridge may need replacing, and in many cases the whole thing.  Tail pieces are less prone to wear and damage, and although they rarely need replacing, their screws and/or mounting posts can wear out.

I can deal with bridges and tail pieces of all kind on both electric and acoustic instruments, and with acoustic instruments I know a few lesser known methods that can improve the sound a little, or even significantly, and contrary to popular belief, there are ways to better the intonation of acoustic instruments. So if You have an acoustic instrument that needs work on the bridge, head over to the acoustics section for more details.

To replace original equipment or after market replacements that fit without modification on electric guitars, adds around 10 minutes to a setup which it will need.  It adds around 30 minutes to an hour to a setup if bridge and/or tailpiece mounting hardware is stripped out or damaged.  There are a lot of custom options for bridges, everything from just better saddles to complete conversions from and to tremolos AKA whammy bars.