1. There is a dispute about whether a person with a severe form of Tum'ah must immerse for Tum'as Keri.
2. There is a dispute about the latest time one may say the morning prayers (i.e. the blessings of Shema and the Shemoneh Esreh).
3. There is a dispute about the latest time one may say the afternoon prayer (i.e. the Shemoneh Esreh).
4. One may recite the evening prayer anytime during the night.
5. If one accidentally misses a prayer (i.e. the Shemoneh Esreh), he may make it up by reciting two prayers when he recites his next scheduled prayer.
A BIT MORE
1. Tana Kama: Even a Zav and a Nidah must immerse for nocturnal emissions in order to say words of prayer and Torah, despite the fact that they will not become Tahor from their more severe form of Tum'ah. Rebbi Yehudah: They are exempt from this immersion, even if they first became Tamei as a result of Keri and only later became a Zav or Nidah.
2. Tana Kama: One may say them until midday. Rebbi Yehudah: One may say them until four hours into the day.
3. Tana Kama: One may say it until nightfall. Rebbi Yehudah: One may say it until Plag ha'Minchah (10 3/4 hours into the day).
4. One may recite the Musaf prayer the entire day, but he is called negligent (see 28a) for reciting it after seven hours into the day. (According to some texts, Rebbi Yehudah says that one may recite it only until seven hours into the day.)
5. However, if one misses Keri'as Shema in the morning or night, he may not make up for it by saying Shema twice the following time that he is obligated to say Shema.