Can you see Pleiades and Sirius at the same time on the sky, from Greece? I would like to know if you can see the Pleiades and Sirius in the sky at the same time, from Greece?
What time of the year would that be?

And I would be very greatful if someone knows an interactive starmap where I could see how that would look like.
Stellarium is a free planetarium software, and it allows you view the position of stars in the sky at any date.

Sirius and the Pleiades are actually rather close in the sky. On the line of Orion's belt, on opposite sides. So for much of the the winter months, both are visible in the sky. For example in mid-December, they will be visible at midnight, in south-western skies. At the time of writing (8th October) they will be visible in the early morning.

It is a well known starscape, with Orion central, the Pleiades and the V of the Hyades on one side, and Sirus, scorching on the other.

Of course, the Pleiades and Sirius are "fixed stars", so the separation between them doesn't change. There is no time when they approach each other.