
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given a function $y=f(x)$ defined on the domain $I$, if there exists an interval $[m,n] \subseteq I$ that simultaneously satisfies the following conditions: $①f(x)$ is a monotonic function on $[m,n]$; $②$when the domain is $[m,n]$, the range of $f(x)$ is also $[m,n]$, then we call $[m,n]$ a "good interval" of the function $y=f(x)$.
$(1)$ Determine whether the function $g(x)=\log _{a}(a^{x}-2a)+\log _{a}(a^{x}-3a)$ (where $a > 0$ and $a\neq 1$) has a "good interval" and explain your reasoning;
$(2)$ It is known that the function $P(x)= \frac {(t^{2}+t)x-1}{t^{2}x}(t\in R,t\neq 0)$ has a "good interval" $[m,n]$. Find the maximum value of $n-m$ as $t$ varies.

Present the answer in LaTex format: \boxed{Your answer}
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