CREATE TABLE table_54315 ("PRR Class" TEXT, "Builderpars_m_singles Model" TEXT, "Build date" TEXT, "Total produced" FLOAT, "Wheel arrangement" TEXT, "Service" TEXT, "Power output" TEXT)

What is the build date of the model with PRR Class brs24?
SELECT "Build date" FROM table_54315 WHERE "PRR Class" = 'brs24'
SELECT "Build date" FROM "table_54315" WHERE "PRR Class" = 'brs24'