This paper investigates the congestion relief potential of staggered work hours (SWH) schemes for public transit lines. An ex-ante evaluation framework is developed, building on the combination of a hybrid public transit assignment model with a travel demand management module to simulate the impact of SWH schemes on travel demand and public transit congestion. The key performance indicators capture not only congestion relief benefits, but also rescheduling costs for users. The methodology is applied to the RER A heavy rail line in Paris, the busiest public transit line in Europe. We find SWH schemes to entail congestion relief benefits, as intended, even matching up with telework policies (in that shifting one peak trip produces benefits equivalent to cancelling one morning trip). Yet, such benefits remain limited, adding up to around 20% of total crowding costs for the morning peak period at most. Furthermore, substantial rescheduling costs are involved: decreasing the total time standing by one hour implies shifting fifteen trips also by one hour. Regarding design, we find that shifting few users by a large amount of time is usually more efficient than shifting many users by a shorter amount of time, as the latter may even prove counterproductive by just moving the peak to some other time in the morning. Moreover, we find that focusing the deployment of the SWH scheme on the biggest trip attractor-here the CBD station of La Défense-yields results similar to a deployment over the whole line (for a similar total timeshift). The developed ex-ante evaluation framework could therefore provide guidance as how to improve the design of SWH schemes in the future, in particular in times of social distancing and need for reduced crowding.