For context, in wired chip-to-chip communication electronics, femtosecond variations are (statistically) measurable. Picoseconds are rather pedestrian. A 56 Gbaud signal has a single-symbol duration of about 18 picoseconds and perturbations on the order of 1 picosecond are rather large 5.6%.
Not to downplay the achievement of the article or the innovation in fusion physics and engineering in general, just a bit of context for the timescales.