Adding treatment groups via metadata to Seurat object?

I’d like to add metadata to 6 individual Seurat objects so that after I merge the objects into one, I can later label or split by using these identifiers. For example, I’d like to append an age group and then interval across these 6 objects. For adding an interval, I’ve tried using the below:

AddMetaData(control, metadata = 1hr, col.name = Interval)

However, this error will occur:

Error in .AddMetaData(object = object, metadata = metadata, col.name = col.name) : 
  object '1hr' not found

Appreciate any help, thank you!