hmm; I'm sure you are on a satellite link.
Most of us have a setup likeisp====modem===(router)== . . . == systems
the == are wired connections while the ... implies a possible wifi connection.
With a satellite link, you are more likeisp .[a].. satellite ... your antenna ===modem===(router)== . . . ==
which places at least two radio links [a]+ in your path assuming you wired the system to the router.
Radio stuff is touchy (btw: I did sortwave radio in high school) and there are many reasons why it works one day and not the next, or works daytime but not at night. I suspect you are in a rual setting. Are there ANY tall buildings in the path the antenna is pointed (would guess not); trees? Can you disclose your location (city/state). Weather can also be a factor. You could also have a high utilization factor in your neighborhood (ie: lots of users) which creates 'contention for access', especially when everyone comes home from work or the weekends.
Here's a WiKi on Satellite Internet for background.
I know Verizon has satellite access for laptops;
AT&T + Sprint