The metric registered days counts for how long a particular user or group is active in the network. Since it can be calculated for individuals, it is of ego-centric scope. It is proposed by Viegas et al. (2004), Smith et al. (2009) and Viol et al. (2016).
For the calculation of the metric $rd$ of the user with the id $uid$ the following query is needed:
rd(uid) := SELECT NOW() - date FROM nodes WHERE id = uid;
On the one hand a recently registered user is called occasional user according to Holtzblatt et al. (2013), who has not yet contributed to the network. On the other hand old users tend to have a reputation in a network and are well known. They can exert influence over other members based on their reputation. It should be noted that the user activity over time should also be considered as an old user may have gone inactive over time.
Smith et al. (2009) relate users with a short registration time to question askers and a low connectedness within the network. They occasionally post content, but do not engage in extended discussions. Since such users are newly registered, they do not have a lot of relationships. They still have to connect and build relationships in the network. Therefore it indicates no or a low amount of Social Capital in the network. However, early adopters of the network have a large number of social contacts and a wide array of interactions according to Scott et al. (2012). Thus they form social relationships and strong ties, which is a sign of Bonding Social Capital. As there is no information about the structure of the relationships and the user's position in the network, a statement about Bridging Social Capital is not feasible.
For an analysis of the network and its users a minimum activity is required (Riemer et al., 2015). A more in-depth look is available with the metric user activity over time.