Hi how do you unlock pyramid timed setting achievement? I set it to timer mode on achievement ...

Start a pyramid game, open menu and options while in game, timer on/off should be the first in the list. When you change it, a new game with the new setting will automatically start. Timer should appear on top right.

One game should be enough for the achievement (I got it years ago so I cannot verify this last point directly).

There is not a setting that will prevent the achievements from unlocking. Check his achievement list to see if the achievements are showing unlocked and he is just not receiving the notification when they do. If this is the case you will want to do the following.
From the dashboard go to Settings>Preferences>Notifications and be sure that both "Show Notifications" and "Play Sound" are checked. Also, if his online status is set to busy he will not receive the notifications of the achievements being unlocked, to check
this do the following. Again, from the dashboard go to Settings>Preferences>Online Status and make sure he is set to anything but "Busy". Hope this helps.

I think the 50 point achievement has a certain unlock timer. I've noticed that if I do one after 6 PM Eastern it won't trigger. Then if I click it the next day it will unlock from a previous day achievement.

This is ridiculous. Found a "Temporary" and RIDICULOUS "Fix" for this problem.

I've saved my game before an achievement and i've tried changing the "System Settings"

1st setting (My Setting) - Languaje & Location, Spanish/Spain. The Achievement not unlocks

2nd setting - Languaje & Location, German/Germany. The Achievement not unlocks

3rd setting - Languaje & Location, French/France. The Achievement not unlocks

4rd setting - Languaje & Location, English/United States. The Achievement UNLOCKS

I Tried it with the four settings and with the first four story related achievements of the game (You can see it in my profile)... and they only unlocks if I'm playing with the settings English/United States.

So... right now, If I want to unlock story related achievements, I must "play" those games In english even if it's not my main language (but I can defend myself). But... what about the people who don't speak english? They don't "deserve" to unlock achievements?

This need a fix ASAP

The Vidmaster achievements were a list of achievements that you had to unlock in order to unlock the armour set via Bungie.net. So because Bungie has nothing to do with Halo anymore, the option isn't there which is why 343i is unlocking it for everyone over
time. So CISphil is right on that.