Systemli's Matrix home server instance has a default retention time of 30 days. We allow values from 1-180 days. Sadly, this setting is currently not exposed in Element. If you want to increase/decrease this time, do as follows:
curl -X PUT -d '{"max_lifetime": 7}' --header "Authorization: Bearer $your_access_token" 'https://matrix.systemli.org/_matrix/client/r0/rooms/$your_room_id/state/m.room.retention/'
curl --header "Authorization: Bearer $your_access_token" 'https://matrix.systemli.org/_matrix/client/r0/rooms/$your_room_id/state/m.room.retention'
If something custom is configured it should return something like
{"max_lifetime":$number_of_miliseconds}