Splitting the cage to house two gliders until you can introduce them to each other can work but only if the divider is something they cannot reach through - they would grab each other's tails or even bite between the bars if they can reach each other.
If you get two gliders from different sources the 30 day quarantine is recommended which means NO CONTACT between the two gliders until both have had well check ups with a vet and two fecal tests 30 days apart to ensure that neither has parasites to share with the other. If introductions are done before the second fecal testing there is a chance that parasites were in a dormant phase at the first testing and then both gliders would need to be treated if either has parasites and they have been housed together.
Getting a 2nd glider later does not always work out - sometimes 2 gliders are just not compatible cagemates and will fight so that they cannot be housed together - leaving you with two cages and two gliders in need of a companion.
If at all possible get two gliders that are either young joeys from the same breeder, or two that have already been introduced to each other and already are best friends. You will then not need to mess with (or worry about) introductions.
Young joeys that are 8 to 12 weeks OOP are usually quite easy to introduce to each other and very often the breeder will do the introductions for you before you pick them up. If they are from the same breeder you would not need to do quarantine because if either was exposed to parasites - the other probably was too by being in the same household.