There are several configurable options that control limits placed on user reservations. Reservation Timeouts also affect reservations but in a different way.
For basic reservations, there are three configurable options that control the duration of a reservation. These settings are configured as attributes of User Groups. The highest value for each setting is used from among all of a user's group memberships.
For imaging reservations, users are automatically given at least a 12 hour initial max duration after which their normal max extend and total max times are applied.
The reservation duration limits do not apply to server reservations.
The number of concurrent reservations a user may have is controlled by the Max Overlapping Reservations setting which is also an attribute of User Groups. For an administrator to be able to control this setting, the administrator must have the Additional User Group Permission. The highest value for this setting from among all of a user's group memberships is used. The allowed settings for this field are a bit unusual. The setting can be 0, or 2 or more with 0 meaning the user can have 1 reservation at a time (i.e. 0 overlapping reservations) or 2 or more reservations, depending on the value of the setting (i.e. for 2, the user could have a total of 2 reservations, meaning 2 reservations that overlap with each other). This constraint applies across all of a user's reservations, regardless of the reservation types.