A.T. Robertson Commentary Luke 19:13

"And he called ten servants of his, and gave them ten pounds, and said unto them, Trade ye [herewith] till I come." — Luke 19:13 (ASV)

Trade ye herewith till I come (πραγματευσασθε εν ω ερχομα). First aorist middle imperative of πραγματευομα, an old verb from πραγμα, business. Here only in the N.T. Westcott and Hort in their text read πραγματευσασθα, first aorist middle infinitive (-α and -ε were pronounced alike). The infinitive makes it indirect discourse, the imperative direct.

While I am coming is what εν ω ερχομα really means.