All I could think of doing was filing a bug report.
If, at tier one, not enough clan members visit the citadel in a week, it becomes locked. No one may enter the citadel until five non-probationary clan members re-open it by attempting to visit it. Upon reopening, the citadel will be in a dilapidated state, with only a dilapidated tier one woodcutting plot, but the avatar habitat and other cosmetic upgrades from before the locking will be preserved. Note that the avatar habitats aren't available during dilapidated times, but will be available as soon as the regular citadel state has been restored.
If an insufficient number of clan members visit in the week for upkeep, then upon the build tick buildings become dilapidated. Dilapidation causes the clan's colours to be removed from the wall and the skill plots to function at a lower level. In addition, any resources that may have been allocated to upgrade jobs or customisations go instead into the storehouse and are subject to spoilage upon the build tick, as if the jobs did not exist. Any payments made in previous weeks for those jobs are not lost, and the jobs themselves are not cancelled. If another build tick goes by and not enough members visit the citadel, it downgrades by one tier and remains dilapidated. Any citadel features, such as skill plots, that require the higher tier are removed. The only exception is a Tier 1 Tree, which never dilapidates.
You can see by this screenie the time of the build tick (upper right)...it does not coincide with the daily or weekly tick.
Nor is there any place in the citadel that I can find recording the number of clan mates that have visited.
HOWEVER, it seems very important that we all try to at lease visit, as highlighted in yellow above.