I can define anchors in sequence diagrams (details see Sequence Diagram syntax and features)
@startuml
!pragma teoz true
{start} Alice -> Bob : start doing things during duration
Bob -> Max : something
Max -> Bob : something else
{end} Bob -> Alice : finish
{start} <-> {end} : some time
@enduml |

Wouldn't it be a nice feature for the mindmaps too?
@startmindmap
* root node
{start} * some first level node
* second level node
* another second level node
* another first level node
{end} * another first level node
{start} <-> {end} : an additional relation
@endmindmap
BR Helmut