Measuring your WordPress site’s TTFB won’t mean much unless you have a general idea of what a good time is. The standard TTFB is anywhere between 200 ms to 600 ms, so if you’re in that range, you’re probably okay.
However, the lower this metric is the better. Ideally you’ll want it to be below 100 ms, although this is superior performance and can be difficult if you have a complex website. On the other hand, anything higher than 600 ms is a problem that you should address as soon as possible.