What are the guidelines on the number of hours worked during a week by
salaried employees? Is there a minimum I can expect from my employees?
Some claim working 8:30 to 4:30 with an hour off for lunch is typical
of normal practices today. Is this true?

If you're in the US then 8:30 to 4:30 is not the norm.  The US
Government (the largest employer in the world to my knowledge)
requires 80 hours per pay period, which for a 5 day a week employeee
would be 8 hours a day.  That would be 8:00 to 4:30 with a 30 minute
break for lunch somewhere in there (notice that lunch does not count
towards hours worked).  So if you count lunch that would be 85 hours
in 2 weeks (or 42.5 hours for a typical worker).

I work a 9 hour shift with every other Friday off so my weekly hours
vary (as do many government employees) so the 2 week numbers are more
reliable than 1 week.

I have heard that there are countries in Europe that have a 35 hour
work week as the norm, but I haven't seen it myself.

Salaried employees or exempt employees? Most people assume these are
the same thing, but they are NOT. You can check with your state laws
about hours and wages. In California you can have non-exempt employees
work 8 hours a day for 5 days in a week and not have to pay overtime.
Everyday they are entitled to two 10 minute breaks that you pay for,
and one 30 minute lunch break that you don't pay for (although you
could). The employees must stay at the company property during the 10
minute breaks since you are paying them, but can leave during the
lunch break. So 9:00am to 5:30pm would be "normal" in California. If
the workers are truly non-exempt (executives, managers, or
professionals), then they can work long hours and there will be no
need to pay them overtime.

A minimum you can expect from your employees?  YES.  

As salaried employees, they are expected to WORK a minimum of 40 hours
in one week. In your example of working 8:30 to 4:30 with an hour off
for lunch, that is only 7 hours per day. That is 5 hours short of the
minimum you can expect in one week. The 40 hour work week is standard.
Lunches are unpaid. Employees also get two paid 10 minute breaks, one
in mid am, the other in mid pm.  This scenario, give or take the
details, is standard.

Paying them on the 15th and 30th saves you two payrolls a year. If you
have too many salaried employees, they will become lazy. Cut back
until they are forced to work 2-4 hours of OT each (per week), to
maintain absolute minimum requirements and productivity will increase,
a lot. There's a lot of hungry people out there that would like their
jobs.  Worked for me.

~~Cynthia