Consider the semilinear energy-critical parabolic PDE in $\mathbb{R}^3$
\begin{align}
\partial_t u &= \Delta u + |u|^{4/(n-2)}u = \Delta u + u^5\\
u(0,x) &= u_0\in \smash{\dot{H}}^1(\mathbb{R}^n).
\end{align}

I am trying to understand the smoothing effects of the above flow. Brezis–Cazenave [here][1] proved

Theorem: Assume $q>N(p-1) / 2$ (resp. $q=N(p-1) / 2$ ) and $q \geq 1$ (resp. $q>1), N \geq 1$. Given any $u_0 \in L^q(\Omega)$, there exist a time $T=T\left(u_0\right)>0$ and a unique function $u \in C\left([0,T], L^q(\Omega)\right)$ with $u(0)=u_0$, which is a classical solution of $\partial_t u = \Delta u + |u|^{p-1}u$ on $(0, T) \times\bar{\Omega}$ (in the Duhamel sense).

Moreover, we have:  

(i) Smoothing effect and continuous dependence, namely

$$ \|u(t)-v(t)\|_{L^q}+t^{N / 2 q}\|u(t)-v(t)\|_{L^{\infty}} \leq C\left\|u_0-v_0\right\|_{L^q} $$

for all $t \in(0, T]$ where $T=\min \left\{T\left(u_0\right), T\left(v_0\right)\right\}$ and $C$ can be estimated in terms of $\left\|u_0\right\|_{L^a}$ and $\left\|v_0\right\|_{L^q}$.  

(ii) $\lim_{t \downarrow 0} t^{N / 2 q}\|u(t)\|_{L^{\infty}}=0$.  

(iii) If $u_0 \geq 0$, then $u(t) \geq 0$ for all $t \in\left[0, T\left(u_0\right)\right]$.

Furthermore, for any bounded set (resp. compact set) ${K}$ in $L^q(\Omega)$, there is a (uniform) time $T=T({K})$ such that for any $u_0 \in \mathcal{K}$ the solution of the nonlinear heat equation exists on $[0, T]$.



I would like to understand if one can show further gain in the regularity of solutions to the above PDE. For instance, **is it true that the following integral is finite**

$$\int_t^T \int_{\mathbb{R}^n} |u|^{2(n+2)/(n-2)} dx dt = \int_t^T \int_{\mathbb{R}^n} |u|^{10} dx dt < +\infty$$

for $0<t<T?$. 

**Edit:** Thanks to the comment below, when $T<+\infty$ this follows from the smoothing effect which can be used to show that
$$\int_{t}^{T} |u|^{2p} dx dt \leq C \log(T/t).$$
However, when the flow is global, i.e. $T=+\infty$ I am not sure how to extend the above argument since $1/t$ is not integrable at $+\infty.$


  [1]: https://sites.math.rutgers.edu/~brezis/PUBlications/147-J-fulltext.pdf