The actual runtime setting I want to set is the commandTimeout one. I actually have to put the value with quotes round it to compile.
<openaccess xmlns="http://www.telerik.com/OpenAccess">
<references>
<reference assemblyname="MSW.MAPS.HealthRoster.Domain" />
</references>
<connections>
<connection id="DatabaseConnection">
<!--Server and Database obtained from SettingsManager.ISettings -->
<backendconfigurationname>mssqlConfiguration</backendconfigurationname>
</connection>
</connections>
<backendconfigurations>
<backendconfiguration id="mssqlConfiguration" backend="mssql">
<mappingname>mssqlMapping</mappingname>
<l2CacheEnabled>true</l2CacheEnabled>
<l2QueryCacheEnabled>true</l2QueryCacheEnabled>
<l2CacheMaxObjects>100000</l2CacheMaxObjects>
<ext.db-key-generator.grabSize>250</ext.db-key-generator.grabSize>
<runtime commandTimeout="100"></runtime>
</backendconfiguration>
</backendconfigurations>
<mappings current="mssqlMapping">
<mapping id="mssqlMapping" />
</mappings>
</openaccess>