It's no secret that I've got really low expectations for the latest products of the education system in the states. Most of them would be hard pressed to correctly spell the second person singular possessive pronoun, (let alone know what one is) and the lucky ones might as likely tender ur as a candidate. A lost cause.
But it's an altogether different thing for a college-educated professional in the computer science field to not know the difference between then and than. I'll admit that computer science doesn't cultivate great literary skills (looking at some variable names is proof of that!) but there are two things common to every computer language around: conditional statements, as in "if condition then consequence," and relational operators, a la "x is greater than 3."
Just as the computer would balk at this snippet of hypothetical code
if water.level is less then 3 than open valves
one would think the ever-diligent engineer would not use sentences like "we would end the seminar no later then Friday noon to provide for return travel." There isn't any condition and consequence, so then is inappropriate. There's a relationship with Friday being established, so it should be "no later than Friday."
Before I reach for my asbestos shorts, let me extinguish one flame: "Lay off, Pierce! A lot of these engineers are from overseas; you're unfairly coming down hard on them." My retort and riposte: that's right; they do. And to be honest, I do cut them slack. Or would, except they aren't the ones making these mistakes. It's the plain ol' English-as-an-Only-Language types with no excuses that do.
Guys (and girls!) ... letting social graces slide is one thing—it's part of the geeky thing. But your job is communication, a little bit of remedial English isn't going to hurt.
Just to point you in the right direction,