I know you start the game when Mario becomes visible, but I cannot find any settings to offset the timer by that amount. Help anyone?

The original version of llanfair does not support having a delayed start timer. If you want that, you can use a fork of llanfair made by Gered, which has many of the extra functionality people are used to with livesplit. On there you can get an attempt counter, delayed start and sum of best. Since the original version of llanfair isn't currently being developed, I would recommend that everyone switch to this version: https://github.com/gered/Llanfair

Thanks!