Space and time in general relativity are but inseparable axes of the same spacetime. But, unlike completely interchangeable and real space axes (e.g. "length, width. depth"), the time axis is slightly special: it's counted as imaginary (see Minkowski space: the distance contracts along the time axis). But otherwise it's an axis like width of height or length.
Quantum "particles" are also "waves", that is, they behave a bit like both, but not exactly like your normal grains of sand or water waves. Like particles, they are "separate", so you can count electrons or photons, and can't cut them in half Like waves, they are wavy and fuzzy, without a sharp edge or border, and interact like waves. When one wave's hump meets another wave's trough, they cancel out ("destructive interference"). When two humps meet, they reinforce each other, resulting in a bigger hump ("constructive interference", yes, sounds ironic).
This is easy to imagine in the space domain, with normal waves that go, say, "up" and "down". With experiments with photons the waves represent the strength of the electromagnetic field, and the interference pictures are ring-like.
Now replace one of the dimensions of the ring with time. This will mean that instead of e.g. darker / brighter circles or stripes on the picture, you will detect "bands" or "stripes" of higher / lower intensity spread over time. Intensity changing over time is oscillation. E.g. air pressure oscillating over time is sound. Electromagnetic field oscillating over time is radiation: radio waves, light, x-rays, etc.
So the experiment managed to let two photons through "slits" in time rather than in space, by opening a "hole" for them to pass and then closing it back really quickly, so that two photons would pass the opening really close in time to each other. This is similar to how the typical double-slit experiment puts slits (or holes) really close by in space, so that the photons can't be far away from each other while interacting.
Then they registered the interference picture, which, AFAICT, was a burst of various electromagnetic frequencies (a "spectrum"). Each photon has a very well-defined frequency (or wavelength, or color, for visible light). So seeing a variety of different frequencies ("colors") would be a tell-tale sign that interference happened, producing multiple "stripes" in the time domain, not space domain.