Connecting unprecise columms With PowerBI

Hello

i want to connect two spreadsheets. One Spreadsheet has more rows than the other. Each spreadsheet has an time stamp on which the connection should happen. The problem is that the time stamps are not equal. Every time stamp of the small spreadsheet should be connected with the next time stamp of the big spreadsheet. In the pictures below you can see the two spreadsheets with a red box around the data which should be connected. 

Small spreadsheet: https://www.bilder-upload.eu/bild-e5b730-1556007354.png.html

Big spreadsheet: https://www.bilder-upload.eu/bild-807077-1556007149.png.html

Thank you in advance