Query: Approximately how long did Napoleon take to prepare another Danube crossing after his defeat at Aspern-Essling?
Context: After the setback at Aspern-Essling, Napoleon took more than six weeks in planning and preparing for contingencies before he made another attempt at crossing the Danube. From 30 June to the early days of July, the French recrossed the Danube in strength, with more than 180,000 troops marching across the Marchfeld towards the Austrians.