How many hours/week does it take to do reasonably well in law school.
(I ask because I am an older potential student with a family.)
   Is it possible to do well in law school through intensive daytime
study, with most evenings and weekends free, or is this a ridiculous
idea? Thanks.
   (Note I am not asking about the difficulty of the work, only about
the amount of time required, assuming I am capable of doing it.)

It all depends, quite frankly, on what you want to do with your law
degree.  If you are content with just graduating from law school and
maybe passing a bar exam somewhere (or not) and maybe being a solo
practioner or a member of a small firm, then sure, you can probably
manage to take a more relaxed approach.  (This assumes you are not
some kind of genius.)

On the other hand, if you aspire to work in a large firm or be a judge
or a law professor someday, you will need to go to a Tier One law
school, make law review, and graduate in the top ten percent of your
class.  Unless you are a genius, you will not be able to do that with
a leisurely approach.  For 99% of law school students, achieving those
benchmarks requires continual, exhaustive study.  You will also
absolutely need a supportive spouse, understanding children and an
alternative income source since you very likely cannot work, even
part-time, and ?make the grade.?

Please also remember the general rule that your first-year law school
grades will affect the rest of your life.  Here's why: your first year
grades are the metric by which you will be judged when applying for a
second-year summer job (since second-year grades will not be out by
the time you apply and are accepted).  Where you work your second year
summer is a very good indication of where you will practice after you
graduate--if you work in a large prestigious firm as an intern during
2L summer and do well, they will likely make you an offer for after
you graduate, and your first job sets the tone for where you practice
after that.  If your first job right out of law school is in the
public sector or a small firm because that?s the best you could do
because your 1L grades were average, it is almost impossible to
"upgrade" to a better firm, an in-house position, a law professorship,
or a judgeship.  That first job (unless you spend a few years doing
grunt work at the DA's office and get a BUNCH of trial experience)
will literally shape the rest of your career, and that first job is
decided by your first year grades.

So, in my opinion, there?s no room for a leisurely approach unless you
are (a) a genius or (b) not concerned about the type of practice you
have and your income level.  Note that some of what I have said can be
modified for third year IF you already have a job.  Many students do
coast during 3L for that reason.

Having supported my spouse through law school, I'd add that the
majority of the work is simply finding, reading, and analyzing cases
in preparation for class.  This can take a long time - especially
since many of them are long and very detailed.  Also, more and more
law schools are putting an emphasis on group work/group study so
you'll have to have time set aside for working with others (who may
not be as interested in having evenings free as you are).

That said, many law schools are also starting programs to support
"nontraditional" students, including people coming to law as a second
career and those with children.  However, I would say that law is a
full-time graduate program, meaning that it will take as much time as
you can afford to give it. No one in my spouse's program had a job
outside of school except in the summer.   These observations also hold
true for the dozen friends I have who've been through the process.

As Ipfan notes, much of it depends on you.  If you are a fast reader
and have a natural affinity for legal research (this is a skill!),
analysis, and discourse, you will spend less time on your work than
the average.  But personally, I wouldn't attack law school unless I
were willing to sacrifice a lot.

I'm afraid this isn't too helpful to you, but I thought I'd put in my
two cents anyway.  Good luck with your decision!

- Librariankt