Running time of Shamir's secret sharing scheme
Is the running times of corresponding steps true?


No. 


Step 3 of the dealer has to be executed $n$ times (once for each party) with each execution taking $O(t)$ time. So it must be $O(t\cdot n)$.
Step 4 of the dealer needs $O(n)$ to distribute each share to every party.


I count $O(t\cdot n)$ as the overall time complexity for the dealer. Of course, you can make it more specific, because the time of all calculations depends on the size of $p$.