how is it possible to measure delay, rise time and fall time in xschem?

The only way I know, would be to make a transient analysis and measure it in a plot... But its not exactly accuracte...

couldn't be defined variables like for example delay='vo-vin'?

@milad Yes, you can measure rise times and delay sin ngspice. See paragraph 15.4 of the ngspice user manual.

15.4 Measurements after AC, DC and Transient Analysis

Below example calculates a rise time of signal v(z[6]):

.measure tran trise 
+ TRIG v(z[6]) TD=10.5n VAL=0.1 RISE=1
+ TARG v(z[6]) TD=10.5n VAL=1.7 RISE=1

the above statement measures the time v(z[6]) takes to go from 01V to 1.7V in the first rise after 10.5ns. see below image, the value printed from ngspice matches the Measurement done on the plot. If you use two different signals in above

.measure

you can measure delays (for example from rising clock edge to rising flip flop output)

thank you @Stefan Schippers