Modeling Conversion Events in a Data Warehouse
This is commonly represented with an accumulating snapshot fact table or timestamped accumulating snapshot fact table. Accumulating snapshot tables model events in progress for business processes that involve a predefined series of steps. The timestamped. 

You'll have a date key in the table that represents the date the opportunity hit each stage. If you need to reproduce what pipeline looked like on a given day or track the fact that an opportunity went into and out of a stage multiple times, you might need to consider the timestamped accumulating snapshot.