Change the example from 5min to 12h

Have a purge job running every 5min is probably not something we want to advise admins to do as a sort-of default.

docs/sample_config.yaml

@@ -387,17 +387,17 @@ retention:
   #
   # The rationale for this per-job configuration is that some rooms might have a
   # retention policy with a low 'max_lifetime', where history needs to be purged
-  # of outdated messages on a very frequent basis (e.g. every 5min), but not want
+  # of outdated messages on a more frequent basis (e.g. every 12h), but not want
   # that purge to be performed by a job that's iterating over every room it knows,
-  # which would be quite heavy on the server.
+  # which could be heavy on the server.
   #
   #purge_jobs:
   #  - shortest_max_lifetime: 1d
   #    longest_max_lifetime: 3d
-  #    interval: 5m
+  #    interval: 12h
   #  - shortest_max_lifetime: 3d
   #    longest_max_lifetime: 1y
-  #    interval: 24h
+  #    interval: 1d
 
 
 ## TLS ##

synapse/config/server.py

@@ -948,17 +948,17 @@ class ServerConfig(Config):
           #
           # The rationale for this per-job configuration is that some rooms might have a
           # retention policy with a low 'max_lifetime', where history needs to be purged
-          # of outdated messages on a very frequent basis (e.g. every 5min), but not want
+          # of outdated messages on a more frequent basis (e.g. every 12h), but not want
           # that purge to be performed by a job that's iterating over every room it knows,
-          # which would be quite heavy on the server.
+          # which could be heavy on the server.
           #
           #purge_jobs:
           #  - shortest_max_lifetime: 1d
           #    longest_max_lifetime: 3d
-          #    interval: 5m
+          #    interval: 12h
           #  - shortest_max_lifetime: 3d
           #    longest_max_lifetime: 1y
-          #    interval: 24h
+          #    interval: 1d
         """
             % locals()
         )