If you have either a Premium or Lifetime Memories Membership, you can add as many Memories, and as much media, to your Timelines as you like. There are no limits.
If you have a free Memories Membership, you can add up to 1GB of media and descriptions in total (while Plus membership offers 5Gb in total), across all your Timelines. So, the specific number of Memories you can add to your Timelines will be limited by the size of the photo, video and PDF files you include. This article will tell you how you can upgrade your membership plan.
On the app, each memory card is limited to a maximum of 10 photos (regardless of the storage plan). So if you're intending to add more than 10 photos, you have to create another Memory card or log in on the web to bulk upload your photos. Please view this article with regards to our bulk upload feature.