Hi Anjali,
Based on scope,Typically timeline for implementation are
APO-DP : 16-26 Weeks.
APO-SNP : 22-35 Weeks
Challenges -
Master Data Cleanup and Maintenance
Change Management - People/Process/Technology.
Project scope creeps.
and now IBP or Standard APO or APO on Hana etc
Advantages - I suggest you read below thread.
General Discussion - Why to choose APO over R/3 for planning?
Hope this will help.
Thank you
Satish Waghmare