Not a very
And of course short as the opposite of long.
Sometimes
a short period of time that is available for a particular activity (LDOCE)
but without more context I'm not sure it fits your situation.
Or one can just quantify time as an uncountable noun:
- we won't have much time (look for definition 5)
- there won't be a lot of time
I can't think of any English term that is regularly used for this – at least, not in a noun form.
As Steve Ives mentioned in his answer, this is how I would ask the question:
What time are you leaving?
The term departure time is grammatically correct, but that expression is normally reserved for transportation: planes, trains, and busses. And it generally refers to the time that the conveyance departs (everyone knows that passengers must arrive earlier than that so they can all board before departure.)
If you want to tell your friends that you'll be leaving the campus at 5 o'clock, you'd say something like:
I should be leaving the campus around five.
or:
I should be done at the campus around five.
You'd only use departure time if you were trying to be funny by making something ordinary (i.e., leaving the campus) sound very official:
My departure time from campus will be 5 o'clock.
I could say a father saying this to his young children, if they were leaving for a trip the next day:
Our departure time will be 8 AM.
but that would be overly formal and therefore deliberately humorous. A more natural way to say it would be:
I want us to get out of here by eight.
or:
Let's be pulling out of the driveway before 8 AM.
The same holds for arrival time. We typically say something like:
We should be there a little before 10.
not:
We have a 9:55 estimated arrival time.
unless we are trying to be somewhat humorous by being overly technical.
Best Answer
Let's analyze, but focusing only on the lecture example, and let's assume, in order to simplify the language, that we all know the lecture is today and we're only asking about time. So here are three options -- your two, followed by a commonly used third:
Note first that since all three are widely used, all three are acceptable. (Literally -- because they are accepted.) And that goes for both the UK and US, and for written and spoken English.
HOWEVER, when you multiply it all out -- the three forms of words, two countries, two delivery modes --- the resulting TWELVE possibilities do have different flavours (or flavors :-) ) and it's useful to know the impact each will have. Here is a rough outline:
This is the most formal of the three, and most likely to appear in written British English. It would sound most stilted in spoken American English. The placement of the preposition "at" at the front probably stems from an old, but silly rule that one should never end a sentence in a preposition.
This is perhaps the least formal, so reverse the above in terms of formality. Now there is an argument that this form is simply wrong since it is committing a category error. A lecture is a lecture, not a time. So it makes no sense to ask what time a lecture is. By contrast, lectures can be at a time, hence forms #1 and #3. But again, this form is widely used, and so it cannot sensibly be said to be wrong. The meaning of language is its use in practice, an' all that Wittgenstein stuff.
Were it not for the silly "don't end a sentence in a preposition rule" (stemming, I think, from Latin translation standards) this form would, to me, be the best middle road. It is strictly grammatically correct (versus #2 which is not), but it avoids the stilted formality of #1.