measurement range of tdc
The TDC7200 datasheet specifies:


  (p1) Measurement Range:
  – Mode 1: 12 ns to 500 ns
  – Mode 2: 250 ns to 8 ms


and

(p5)
+-----------------+------------------------------+-----+-----+------+------+
|      Param      |         Description          | min | typ | max  | unit |
+-----------------+------------------------------+-----+-----+------+------+
| T1STARTSTOP_Min | t_min between Start and Stop |  12 |     | ns   |      |
| T1STOPSTOP_Min  | t_min between 2 Stop Signals |  67 |     | ns   |      |
| T1STARTSTOP_Max | t_max between Start and Stop |     | 500 | ns   |      |
+-----------------+------------------------------+-----+-----+------+------+


table adapted from datasheet, formatted thanks to online tool

So you can see that for mode 1 the range is defined as t_min between Start and Stop up to t_max between Start and Stop.

Within those boundaries the measurement will be returned with a resolution:


  (p1) Resolution: 55 ps


So from a high-level timing longer than 12ns and shorter than 500ns can be measured with a resolution of 55ps (in mode 1), for mode 2 this is a function of the SPI clock provided to the TDC.