Start cold, end warm = good rule of thumb. As Jake said though, slightly higher temperatures such as 20C are not going to hurt things. In fact, using S-05 in a "winter warmer" type beer, you might almost find that the additional esters and fusels from a warmer fermentation add to the flavour and "warmth", although that's not to say that excess is going to be entirely positive.
On the other hand you might want to consider over-pitching a little to speed things along... I've done it before, but again - it's prioritising speed over quality to some degree. And again: don't overdo it.
And one more thing: if you're using S-04 at anything above 18C, definitely use a blow-off tube. That stuff has redecorated my ceiling a fetching shade of dogshit brown on more than one occasion.