Overview
Budget Cycle time spans provide the budget cycle period definitions to be used and applied when sourcing, aggregating and calculating available budget funds to be applied for budget control purposes.
A budget cycle time span is first associated with a specified accounting or financial calendar (as setup in the general ledger), with the individual budget cycles used for budget control firstly defined by the ‘length of budget cycle’ setting which determines if the budget cycles are then auto-populated if set to ‘map to accounting year’, or manually defined if set to ‘specify number of periods’.
Typically, Budget Cycles are setup to align with an organisations financial years and periods as shown by the setup in the screenshot below.

Assign Budget Models to Budget Cycles
Budget Cycle time spans provide the budget cycle period definitions to be used and applied when sourcing, aggregating and calculating available budget funds to be applied for budget control purposes.
Each budget cycle period definition within a budget cycle time span then needs to have a specific Budget Model associated with it to specify where budget values will be sourced from when calculating available budget funds during that budget cycle.
The screenshot below is taken from the same system and company setup as that of the example budget cycle time span setup screenshot in the section above. Here you can clearly see how the budget cycle time span and underlying budget cycles have been selected, with the budget model from which budget values are to be sourced for that specific budget cycle then specified alongside them.
Note: only one budget model can be associated with a budget cycle.

Further Reading
Further information on Dynamics 365 Basic Budgeting and Budget Control is available on the Microsoft Docs and Learn Docs sites via the URLs below and should help to provide further background and context to aid survey question completion.
Budget control overview – Finance | Dynamics 365 | Microsoft Docs