from my way of thinking u can use the 90 day visa when u like within the 2 dates on it . . its till 90 days from when u enter thialand . u just need use the visa by 11 dec 2024 .which u will if u are enter thailand in nov 8 2024 .so no problem and no issues .
i use nong khai . there is a bus goes from udon thanni to Vientiane .its easy and cheap. best cross early morning as it gets busy . 35 us dollars for the visa . i aint had to stay over before but seems u do now haha,still it will be fun have a few nights in Vientiane
only had a issue once when i had entered thailand 3 times in 6 mths. but luckily i did have my home flt booked to let me in ,other 2 times they didnt even ask .