To work out velocity, position or time, the relationship V=dx/dt or V=∂x/∂t where ∂x is the difference in position (in a specific direction), and ∂t the corresponding difference in time.
t1=2.0, t2=4.0, t3=13 and t4=17 give 4 time values, but position (x) values are needed for the positions.
A function like x(t)=a0+a1t+a2t^2+a3t^3+... etc is needed to relate time and position.
Alternatively we need a velocity function v(t) from which position can be calculated using integration and initial conditions. x=∫vdt between specific limits for t.