Mojang is performing scheduled maintenance on Monday, April 13th. All their servers will be down approximately 11pm to 3am MST. I am unsure exactly what that means for Sandlot, but there's a pretty good chance you won't be able to play Minecraft on any servers during that time. If you connect to Sandlot before they turn the servers off, you can probably continue to play during the maintenance, but if you disconnect, you will most likely not be able to reconnect. https://mojang.com/2015/04/planned-maintenance-tuesday-april-14/