If I place an order today, what is the lead time for any system (standard or custom)?

It depends on the model # or series.

Also, lead times are typically longer during the 4th quarter.

Standard enclosures are approximately 2-4 weeks and sooner if at all possible.  End of year, approximately 4-6 weeks.

Custom enclosures depend on the complexity.

The minimum is 6-8 weeks, 10-12 weeks, or 15-20 weeks depending on the time of year and the complexity.  These times will be sooner if at all possible.  They have to pass Factory Acceptance Testing.