To create a Billing Schedule:
1) Navigate to Lists > Accounting > Billing Schedules > New
2) Name your Schedule
3) Initial Amount = 50 %
4) Initial Payment Terms = Net 30
5) Recurrence Frequency = Custom
6) Recurrence Count = 1
7 ) Navigate to the custom line add the criteria below:
-- Count = 30
-- Units = Days
-- Relative to Previous = Yes
-- Amount = 50.0%
-- Payment Terms = Net 30
Once you have saved the Schedule you can apply it by navigating to your Sales Orders > Billing tab > Billing Schedule> Select your Schedule.
NetSuite currently does not provide the ability to have two terms added to one Invoice. This feature is currently captured in enhancement 175478.