something I should have asked

It should be 30 days since all international border crossings are supposed to provide a 30 day visa upon arrival. The only exception that I know of for foreigners other than some ASEAN neighbors are for Japanese nationals who receive a free 2 week visa upon arrival.

Keep checking the little ink stamps in your passport. You should have one from Lao immigration dated the same date as your VOA. It will give your arrival date and an admitted until date of...............either 14 or 30 days later.
Last time I entered at Friendship Bridge the little red stamp was 4 pages in front of the VOA page. They just plonk the stamp anywhere there is a free space. Check thoroughly it'll be there.

It will say when good until which will probably be 30 days from the day you entered the country.

When I last entered Laos in 2005 the good until day was December 28. However the 8 could not be seen well. Then when I was leaving the country on December 26 the guard asked for $60. Of course I did not know why, then he said because I overstayed my visa by 6 days. I then showed him my wifes passport and visa stamp which had the same entrance date and CLEARLY showed a good until date of December 28th. His $60 was quicky gone!

My last visa I got at the friendship bridge about 2 months ago didn't say how long it was for either. But it's 30 days. I left Laos just before the 30 day period. It used to be only 15 days but that's changed now.

yep no. 2 is right just look in your passport. mine was a few pages away too. but just in case he really forgot it is usually 30 days.

I met a lady in China who said she did not get the date stamps when she entered, had to pay a big fine or go back to point of entry. Yes, triple sheck all pages there must be an exit date.