Thanks Frank for the response.
Yet, after reading the arrow paradox and Aristo's response to it in wikipedia i think there is a difference just like Aristo said. The arrow paradox talks about infinitesimal instances which is something that only exists mentaly, like Aristo said and is different than saying that time has no beginning. If instances were real then the length of a second would be equal to the length of an hour, both infinity. Instances are just a limit that something can 'go towards' but never reach it. A second on the other hand is a real size.
I can imagine space having infinite number of meters, but if someone had to pass an infinite number of meters he had to walk at a speed of infinity at least some time or else he would never reach his destination (and in any given speed he walks at a rate of infinite number of infinitesimal points per second by the way, but that won't help him pass infinite number of meters).
The difference between a meter and a point is the same as the difference between a second and an instant. So if for present to arrive the past must pass then shouldn't the past have only a finite number of seconds?
Another difference is that unlike the arrow which obviously moves, time doesn't have to be infinite so nothing forces us to believe it is and just look for a justification.
And looking at it as a whole, it might be infinate like the space example, but 'now' depends on the past, so 'now' had to 'walk' through time, second after second, which is like the guy walking through space which will never walk infinitae number of meters. And because 'now' did arrive here then 'now' did not 'walk' infinate number of seconds.