A friend of mine who traveled recently claims that I have to exit the airport and re-enter again in order to catch a connection flight that is made of two separate tickets. This will significantly affect the time available to get on the second flight as there is no way to estimate the time you need to pass through security.
Is this information correct?
I have no checked baggage
I've not been to this airport myself, but based on the terminal maps available from the airport website it seems that your friend is correct.
The diagrams are low resolution, but I'm just about able to make out the captions. The map of the first floor isn't relevant to your question. The ground floor shows two arrivals gates (top-left, marked by a box with a left-pointing arrow) and four departure gates (bottom-right, marked by a box with a plane).
There's no indication of any airside passageway between the arrival and departure zones. The only option available seems to be leaving the secure arrivals area and then entering the departure area the same as if it were your first flight. This will involve passing security again.
If you have checked baggage, then no. Ryanair only offers baggage transfer at 3 airports (Fiumicino, Milan Bergamo and Porto).
It also seems from the answer from @Chris H that there is no airside transit option at Warsaw Modlin airport.
