Based on device tracker Xiaomi Router - Home Assistant that the code is at core/device_tracker.py at 17bf51a855d981b757299be53cdb3ca488176c5b · home-assistant/core · GitHub you can get the uptime, download and upload speed, ram usage, and more data of the xiaomi router.
Although the data has to be pulled from http://your_router_ip/api/misystem/ (just remove devicelist from behind the address)
{"dev":[{"mac":"60:57:","maxdownloadspeed":"12571012","isap":0,"upload":"8422003732","upspeed":"1585","downspeed":"1704","online":"79312","devname":"nombre-pc","maxuploadspeed":"9673042","download":"157019574734"},{"mac":"3E:5E:","maxdownloadspeed":"12674244","isap":0,"upload":"817595557","upspeed":"0","downspeed":"0","online":"15140","devname":"3E:5E:","maxuploadspeed":"14186270","download":"4152297040"},{"mac":"5C:52:","maxdownloadspeed":"6628704","isap":0,"upload":"212096181","upspeed":"0","downspeed":"0","online":"123547","devname":"5C:52:","maxuploadspeed":"124890","download":"4053559383"},{"mac":"AC:E0:","maxdownloadspeed":"15474398","isap":0,"upload":"41057585","upspeed":"0","downspeed":"0","online":"0","devname":"DESKTOP-","maxuploadspeed":"170705","download":"4003807941"},{"mac":"00:F6:","maxdownloadspeed":"2577550","isap":0,"upload":"1140242228","upspeed":"0","downspeed":"0","online":"57583","devname":"Mini","maxuploadspeed":"104618","download":"3890267699"},{"mac":"D4:F5:","maxdownloadspeed":"3830840","isap":0,"upload":"928015750","upspeed":"10","downspeed":"10","online":"5421679","devname":"Mini","maxuploadspeed":"69688","download":"2643289802"},{"mac":"A4:97:","maxdownloadspeed":"15470039","isap":0,"upload":"137399418","upspeed":"0","downspeed":"0","online":"0","devname":"DESKTOP-","maxuploadspeed":"632588","download":"15029763451"},{"mac":"C2:A1:","maxdownloadspeed":"14940879","isap":0,"upload":"410946768","upspeed":"0","downspeed":"0","online":"0","devname":"210","maxuploadspeed":"492704","download":"10593123223"},{"mac":"DC:A6:","maxdownloadspeed":"18121822","isap":0,"upload":"34179895084","upspeed":"1891","downspeed":"1177","online":"4388700","devname":"HA","maxuploadspeed":"11949019","download":"18923516664"},{"mac":"","maxdownloadspeed":"0","upload":10651912253,"download":9331555485,"ip":"","downspeed":456,"online":"0","devname":"Others","maxuploadspeed":"0","upspeed":364}],"code":0,"mem":{"usage":0.6,"total":"512MB","hz":"1333MHz","type":"DDR3"},"temperature":0,"count":{"all_without_mash":46,"online":13,"all":46,"online_without_mash":13},"hardware":{"mac":"28:D1:","platform":"R3600","version":"3.0.22","channel":"release","sn":"00000"},"upTime":"7565164.54","cpu":{"core":4,"hz":"1.4GHz","load":0},"wan":{"downspeed":"3349","maxdownloadspeed":"18121867","devname":"nil","upload":"74866227413","upspeed":"3853","maxuploadspeed":"14688798","download":"620019270360"}}