I trade the London session every day and I can tell you that after DST is over, London session opens from 9 AM. However, during DST London opens by 8 AM.
DST or Daylight Savings Time is when Nigerian time is the same as London time but after DST Nigerian time becomes ahead of London time by 1 hour. DST is from the start of March till october ending every year.
To cut the long story short, during DST Nigerian forex traders should wake up early to trade the London session open by 8 AM. After DST, Nigerians should wake 1 hour later to trade the London open by 9 AM.