The inside of the watch 発言しました don't be late and I think it meant that they would be back on oct. 5 to have there bodies back または the 日 their mother died...
What it means is that not to forget why there on their jouney to get there bodies back,and its the 日付 when they tried to transmute their mom,thats why Winry was so suprised によって what was in it.
It's the 日 Edward burns their house right after Edward get the tittle. It shows their determination of not turning back and 移動する on toward their journey in seeking the ways of returning back theirs body.
they explain it later on.. but yeah,it says "dont forget Oct. 3" and Ed wrote it on the 日 he and Al burned their house down. Ed claimed to have written it so that he would remeber not to ever turn back but his father pointed out to him that he really burned his house because Ed didnt want to be reminded.yeah..i'll shut up now... O.O