Perez Anda Gil Camina. Tonto Es El Que No Adivina. 

Its ok. but in spanish i dont know anyone who say "walk for 3 minutes" usually we say walk arround 200 metres. or 3 blocks for example. idk. perhaps some countries say it "walk for 3 minutes" but its hard to know,. my speed its diferent than others you can walk faster than me.  so is confused. the simple way is in blocks. (in spanish) "Camina 2 cuadras 3 cuadras. o 200 metros 300 metros)  my english isnt the best too. so idk if i put it right. i think the idea its ok. 

When you said. Estudio con mario el lunes. es 100% you will do it, so its a fact you will study with mario. 

when you said estudiare con mario el lunes. perhaps you will o perhaps you will not. you want it but it not 100%, no estas seguro que vas a estudiar con mario. i dont know how to put in english, hehe.