CFR 61.63(c)(4) allows you to add on the CSEL with no specified training time as you may already know. Therefore when you are proficient on the CSEL add on maneuvers your instructor will endorse you for the checkride.
The key is to memorize your maneuvers early in the game. Read the Airplane Flying Handbook, FAA-H-8083-3A and the PTS for the required add on maneuvers. Right down a step by step for each one while cross referencing the completion standards.
Simply put it's all depends on your preparation.
I've had students complete the CSEL training in a few flights when the commit the maneuvers to memory. Other students that needed more time where the ones that showed up to each flight and stated "tell me how to do the Lazy 8 again."
Hope this helps.