can you make more than one trip in a 24 hour period with a rail pass.

No limit. It's fun to see how many trips can be squeezed into one day.

As many as you want - if you're using a SelectPass - for example 4 days in 2 months, you can take as many trains as you want per day you use the pass, but if you take an overnight train starting after 7 p.m., it counts as the next day.