Gap-opening planets can generate dust-trapping vortices that may explain recently-discovered crescent-shaped dust asymmetries in protoplanetary discs. Most previous computational studies of vortices have neglected the time it takes to grow a planet to Jupiter-size, a process that may last more than 1000 orbits. In our work, we incorporate more realistic planet formation timescales into two-fluid (gas and dust) hydrodynamical simulations and synthetic ALMA images of planet-induced vortices. We show that these longer planet formation timescales lead to planets triggering vortices with more elongated shapes, if they even form at all. With low aspect ratios (H/R <= 0.06), Saturn-mass planets induce longer-lived vortices than Jupiter-mass planets. With larger aspect ratios (H/R >= 0.08), vortices are long-lived regardless of planet mass or disc mass because they are less affected by the planet’s spiral waves. We connect our results to observations and find that these elongated vortices still trap dust, but not at the center. With a flatter pressure bump, the dust instead circulates around the vortex. This motion spreads the dust out over a wider azimuthal extent (> 180 degrees) and carries the peak off-center (often by > 30 degrees), two signatures that were both found in the vortex candidate in HD 135344 B. Separately, vortices that migrate outward in the H/R >= 0.08 cases may be able to explain the small cavity size in Oph IRS 48 or the two clumps in MWC 758. Overall, the long lifetimes of vortices with low viscosities suggest that typical viscosities should be higher than 10-5 in the young disc population that has too many gaps not associated with asymmetries.