League of Legends (LoL) Question: Timing of a DoTs first "tick"

So I wanted to ask this because I couldn't find it on LoLWiki. I've been under the impression that with DoTs the first tick of damage is done on application making it so that reapplying it in rapid succession will redo the first tick of damage. For instance, if a champ had 2.0 attack speed at lvl 18 with a Spirit of the Elder Lizard, attacking twice and using a physical damage spell in 1 sec would proc and deal the first tick of SotEL 3 times (50 true damage in that 1 sec). Now is this how DoTs work or am I wrong and does the first tick happen after a second (or whatever the time interval between ticks is)?