When pipeline stages are perfectly balanced (uniform delay) then 1 task execution time in the pipeline is also equal to one task execution time in the non-pipeline.
$Ex: k(stages)=4, n(instruction)=1,cycle time=2ns$
Execution time of pipeline $= 8ns$
Execution time of non-pipeline $= S1+S2+S3+S4=2+2+2+2=8ns$
When pipeline stages are not perfectly balanced then 1 task execution time in the pipeline is greater than one task execution time in the non-pipeline.
Note: If execution time is greater than why we are using pipelining ? It is greater only for one task but when $n\rightarrow\infty$ pipeline performance is way better than non-pipeline.
$Ex: k(stages)=4, n(instruction)=1,cycle time=max(2,6,4,2)=6$
Execution time of pipeline $= 24ns$
Execution time of non-pipeline $= S1+S2+S3+S4=2+6+4+2=14ns$
$\therefore T1\geqslant T2$