I think this can best be achieved using recurring entries. There is an Odoo module for that in version 7, which I am not sure still exists in 8. This way you can define a period time (for example, half a year), a recurring pattern (for example, every month) and tell OpenERP what to do at that point. Most likely this will be creation of invoices or memorial journal entries.

Recurring entries is installed by default in Odoo V8. More information about recurring entries can be found in this post: https://www.odoo.com/forum/help-1/question/how-can-i-split-the-costs-of-certain-invoices-over-several-periods-56045

For revenues view PR 1855 - Revenue Recognition that extends the asset module for sales.