Time references

Question 1

When do you need に？

Answer 1

for numerical time expressions (10:45)
for days of the week (sunday)

Question 2

When do you not use に？

Answer 2

for time expressions relative to the present moment (today, tomorrow)
expressions describing regular intervals (everyday)
for when

Question 3

When can you decide if you use に？

Answer 3

for parts of the day (in the morning, evening)
and for the weekend