"Se mi tiam havus pli da tempo, mi povus fari pli grandan retejon."
Translation:If I had had more time then, I could have made a bigger website.
Is this correct? I don't understand how both halves of the english sentence are in the past tense. Does the presence of tiam at the start of the esperanto really change "mi povus fari" to past tense rather than just "i could do"?