You are actually talking about two different things here. There is tense (past, present) and there is aspect (finished, ongoing, punctual, etc.). In English these are often somewhat hard to tell apart.
Your example has a tense mismatch. The first part is past tense, while the second part is present tense. You can think of it as equivalent to:
I have been at home since 3:00 PM, when you returned.
Which is clearly ungrammatical, because the first part is present tense and the second is past. The "returning" event took place in the past, so your having been home must have occurred in the past as well. So it would be:
"I had been at home (since X time) when you returned...."
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