Can anyone please recommend a non ISP provider router or modem router (FFTP) good at device management, that allows individual devices to be connected and disconnected at various times throughout the day?
Do you have a budget in mind / how technical are you?
Also are you looking for a straight up router/gateway device or do you also want a built in switch and/or access point in the same unit?
The Unifi DreamMachine or Dream Machine Pro might be a gentle step up from the basic all-in-one SoHo routers / ISP supplied devices. The UDM Pro requires external APs while the base model has one (similar spec to the NanoHD/FlexHD) built in. You should be able to go straight from the FTTP provider's ONT to the UDMs WAN port on both models.
The easiest way is probably to create a second wireless network / SSID for the devices you want to time limit and then set a schedule for that network. You could also add a Disney Circle to that VLAN if you wanted finer grained controls.
There's a web site in the USA called SmallNetBuilder that reviews a lot of SOHO equipment and he's pretty objective about how he reviews and tests kit. You could do worse than look there. Just bear in mind he's US based if you reside outside that territory, so exact spec. of the kit may differ (often it's just the PSU.)