Lower bound on running time for solving 3-SAT if P = NP

Is there a lower bound on the running time for solving 3-SAT if P = NP. For instance, is it known that 3-SAT can't be solved in linear time? What about quadratic?

We establish the ﬁrst polynomial time-space lower bounds for satisﬁability on general models of computation. We show that for any constant $c$ less than the golden ratio there exists a positive constant $d$ such that no deterministic random-access Turing machine can solve satisﬁability in time $n^c$ and space $n^d$, where $d$ approaches 1 when $c$ does.