Not every if is a daydream. When something might really happen, Finnish keeps the plain present in both halves — and the present also covers the future:

Real — it might happen	Unreal — imagined
Jos sataa, jäämme kotiin.	Jos sataisi, jäisimme kotiin.
If it rains, we'll stay at home.	If it rained, we'd stay at home.
Jos ehdit, soita minulle.	Jos ehtisit, soittaisitko minulle?
If you have time, ring me.	If you had time, would you ring me?

The endings alone flip reality into imagination. English does the same with rains → rained, will → would — Finnish just does it with -isi-.