Hi @Vaibhav G.,
if you're unsure about the meaning of DCRUM metrics what I suggest is to look at the Dimension and Metrics definition in the Help page. There you'll find a complete list of all the metrics and dimensions with the corresponding description.
Here how to access the Help page (instructions for 12.4.x): go to DMI -> New report and then click on the Help button as shown in the screenshot below:
you'll get the following page:
Hope that helps.
In general, every analyser type will have a threshold that is set in the AMD global config that determines if it is a fast or slow transaction. I could not find the specific setting for SMB like I could for HTTP (which is 8sec). In my environment, looking at the auto-discovered SMB traffic it appears the threshold is 10min. Try hovering over your slow operations column and see if the tooltip gives you a similar figure.