LTSPICE how to use the TSTOP and TSTART in Subckt?
A subcircuit is just another netlist, so whatever is allowed in a schematic, is allowed in a subcircuit. What you can't do is pass time as a parameter, i.e. x=time, because .params are evaluated prior to simulation start.

What you have inside your subcircuit are some behavioural sources which can have time passed in their expressions, expressions which act as functions, and the parameters within can be passed on to the subcircuit (Tstart, Tstop). Passing those parameters can be done by first declaring them globally (in the schematic):

.param Tstart=&lt;...&gt; Tstop=&lt;...&gt;

and then passing these as values to the subcircuit

Tstart={Tstart} Tstop={Tstop}

and the simulation card as:

.tran 0 {Tstop} {Tstart} &lt;optional_time_step&gt;

If I misunderstood your question, please let me know.