What it is to be "passionate" about something (or someone)?
It is to associated THAT thing (or person) with your Past and Future (this is Chitta-Vritti). When you let it water (emotions) your tree of Memories, or when you let it create castles of hopes, dreams, desires, expectations for your future, you are "passionate" about the thing (or person).
Now what about the Present?
Its the moment where the "Gem" lies, that every Yogi aims to get, and thus becomes a blissful SthitaPragya, that, in simple terms, is the one who lives ONLY in the moment of the divine Present. As its only the idea of Present thats absolute, and whether its the "realities" of Future, or perceptions about Past, it all CHANGES!
Its that tiniest moment of Present that transforms the Future into the Past. Its THE point where Past and Future meet on the temporal landscape. Its like Sandhya, the time when of a day meets night, and vice versa (its the MOST auspicious period of a day). Notice that the Sandhya-Kaal is characterized by the color Saffron of the Sun (that signifies the 'Self'). And this same color represents Renunciation & Transformation too. (Why do you think Sanyasis wear Saffron color robes?)
Now practically speaking, how long in span should the temporal sense of "Present" be, so that it remains tangible for an individual?
Of course it should be as small as possible. But how small? Is it 1 sec long span, or 1/2 sec, or 1/4 sec...? This series goes on indefinitely and never reaches Zero! You may have heard of Sages meditating for years. Actually they used to meditate (NOT concentrate), while keep on reducing the "span of their idea of Present" (like the afore mentioned infinite series) to an extent of a Bindu, where the Yoga (meaning "Sum") of Past and Future happens, where "Dvaita" (i.e the perceptions) gets dissolved into "Advaita" (i.e the Awareness)...
So "...what is meant by a Samsaric being dispassionate?"
Indeed, to be dispassionate, you renunciate your clinging toward your own PAST and FUTURE, rather than any material objects or any worldly relation you may have. ONLY when you ACTUALLY live in Present (with SHORTEST possible span), you are LEAST attached with this world.
Living in the tiniest (possible) span of your (absolute) Present, you AUTOMATICALLY follow Dharma, i.e walking the clear, unclogged (by emotions) path of awareness. Like when a wheel "rolls" on a plane surface it physically "touches" the surface only for a moment. Similarly being Dispassionate or Detached is to go on "rolling like a Wheel".
You can reach the answers to your other questions from here.