Time is simple, once you've managed to explain distance, because once you have that then distance traveled by light in a vacuum in whatever time frame you or they use. so realistically its all about distance...
Pressure would likely be a major factor if not the "translator". its highly likely that an alien race advanced enough to have space travel, would likely have a system comparable to the metric system, where almost all units of measurement are connected based around water. Grams, Metres, Celsius and Litres are all relative to amounts of water. Celsius takes 100 increments between the freezing point and boiling point of water at 1 Atmosphere of pressure 1 Cubic Metre of water at 1 Atmosphere of pressure weighs 1 Metric Tonne. etc
The reason they would do this is because having a system such as this makes building space craft, plotting orbital maneuvers and various other space related activities easier. simply put, everything comes down to water:
life (as far as we know it) cannot exist without water
Fuel, in space split water into hydrogen and oxygen and you have fuel for rocket engines.
So if the alien race met humans, and managed to translate enough of each others languages to talk but needed to discuss measurements, then if they could translate the difference in atmospheric pressure then this would acutally become slightly easier...
Maybe they could simply show a graph as too how each of their units are interconnected through water, and then place a weight onto a scale on earth, then so still complex but easier math could translate this... "ah i see your 1 QZ weight weights 946 grams that means that the temperature range of liquid water would be lower therefore etc etc...
And before anyone points out the old adage
There are two types of countries in the world, those with the metric system and those who have landed on the moon
Perhaps need to rephrase it too:
There are two types of countries in the world, those with the metric system and those who don't... but had a space agency that did use the metric system in order to land on the moon
I admit, its not as catchy, but still very very true
The next issues to consider is if the alien race has a Base 10 math system, where the number increments by multiples of 10, humans use this because we have 10 digits on our hands, if for whatever plot reasons its Base 8 or Base 17 then matter becomes even more complex...
They final issue actually comes from how are they going to talk in the first place, many scientists believe it will begin simply by starting with an atom of hydrgen, and stating its name and atmoic number, then working up from there, if they can understand chemistry together then they can start getting even more complex language after that