timers

if we need the time delay for example to be 5 seconds, so it can be the multiple of time base and the preset value? (0.001*5000) or (.01*50) or (1.0*5)
so what is the importace of time base here

Please don't start a new thread with the same question you asked a half hour ago in your other thread.
http://www.plctalk.net/qanda/showthread.php?t=59966

Is this an assignment question for a class? Just in case I'm not going to answer you outright, but lead you into thinking about a couple of scenarios.

If you are using a 16 bit processor then the maximum timer preset you can have is 32767. Some PLCs, particularly those that use BCD integers, have a maximum timer preset of 9999 (or even 999 on some older models). So if the only time base that is available is .001 seconds I think you can see where there would be a serious problem. How difficult would it be to program a five minute delay in that case?
What if the only timebase available was 1 second, what problems can you see that causing? Multiple time bases increase your options. Don't get hung up on it.

To create a delay up to the accuracy you desire.
example:
If you need a delay of 0.5 sec,can you tell me how many different types of combination you can come up?
How about 1.005 sec, what is the best time base you should choose?