There are a good number of indoor courts in the Roanoke area , both  associated with country clubs and independently owned. Please see the RVTA WEB Site Home page  for a link to some of these.
The typical setup as far as indoor tennis is concerned is that a group of compatible players will have an indoor court reserved for a specific time slot of about 1.5 hours each week.
Play is usually doubles.
Prime time slots are between 5PM and 9.30 PM on week evenings.
There is usually not much turnover in prime slots. Some groups have had the same time slot for a big number of years.

Each group usually has a designated captain .

The captain’s responsibilities at the independent clubs are :

1. To collect dues from each member of the group and pay same to the owner of the courts.

2. To ensure there is a quorum from the group or with substitutes for each time period.

It is typically not the captain's job to find a substitute for missing players other than himself but often he has to provide this function.

Each player in a group normally keeps a ready list of potential substitutes so that he can line one up when he is not able to play.

In Roanoke, good, reliable substitutes can be hard to find particularly for specific time slots.
The only way people can be sure of having a quorum in the typical group is when there is very good communication between the players and the captain.
The widespread use of email, answering machines and cell phones does not create a panacea in this regard.
When calling for a substitute on the date of play for example it is seldom satisfactory to leave a message for a potential sub since that person may be out of town. It is better to keep calling the list until a real live player is found who can make a committment. If a sub does find a message on his machine (particularly one that has been there for a number of hours) he should call the requester immediately to confirm that he is still needed and that the person has not already lined up another sub.

A lot of this may seem obvious to the average player but newcomers to "time-slot tennis" always have problems getting accustomed to the dynamics of finding substitutes particularly if they are new to the area and consequently do not know other players.

Newcomers.

These should ask other players they know for help in getting on substitute lists with a view to getting into a regular group with a time slot. They can also call the owners of the various indoor sites.  The home page has a link to independently owned courts and country clubs. It is important to give an approximate NTRP Rating.  A self-rating system can be accessed via the RVTA web site under Leagues or Services.