Hi Khan,
You can change the forward-delay time with the following commands:
For PVST+:
spanning-tree vlan x forward-time y
For MST:
spanning-tree mst forward-time y
But as far as MST uses the Rapid Spanning-Tree algorithm inside the MST region, I believe it uses the above mentioned forward-delay time when connecting to traditional 802.1D spanning-trees, like PVST+ and CST.
Does this answer your question?
Cheers:
Istvan