Clocks went back from 2am to 1am this morning, marking the start of winter time which will end at 1am (GMT) on Sunday 28 March 2021.
The time change means darker evenings and road users have been advised to take extra care as the nights close in.
Road Safety Officer at Mayo County Council Noel Gibbons said: "People will be travelling to and from work or education in poor light conditions during this time of year.
" [They will] also be out exercising in Level 5 … many on unlit dark rural roads, so the annual 'be safe, be seen' campaign is always an important reminder."
The practice of switching the clocks was first introduced in World War I to save energy by prolonging evening daylight in summer.
In 2011, Russia decided to switch to permanent summer time in an attempt to improve citizens' well-being, but shifted to permanent winter time in 2014 after public complaints.
The majority of countries outside Europe and North America do not adjust their clocks.
Researchers at the Royal College of Surgeons in Ireland are arguing that tonight should be the last time Ireland changes its clocks back for the winter.
Dr Annie Curtis is an immunologist and senior lecturer at RCSI where she studies the body clock.
She told RTÉ that the practice of changing the clocks each winter and again in spring-time is outdated.
"That practice really now is becoming archaic - to be switching the time. We do need to lock the clock and stay in one time. The debate is whether we should stay on daylight standard time or savings time."
Dr Curtis argues that standard time, the time zone went into this weekend is the best time to stay in for our body clocks.
"We even see when we enter daylight savings time, an increase in cardiovascular events, so there's a really strong connection between our external environment, our body clocks and our health," she said, adding there are even benefits to your immune system as well.
"We need more light in the mornings because that is essentially what times our body clock, our circadian rhythms," said Dr Curtis.
"It's morning light, not evening light that's really important to allows us to ensure that our body clock is really appropriately timed and synergised with our external environment."
She said this synchronisation is important because: "It is known now to affect mental health, cardiovascular health, obesity... so morning light is really, really important to keep us healthy and well."
A recent survey by the Department of Justice found that Irish people would generally prefer brighter evenings in the winter but Dr Curtis added: "We're going into winter time irrespective of what we do with the clocks and we'll only have seven hours of daylight.
"So we can have that between 8:30 and 16:30 or we can have that between 09:30 and 17:30. If we stay on daylight savings time, come December we're going to have a situation where sunrise won't happen until 09:30 in the morning. Ok, we do get that extra hour from 4:30 to 5:30 but in reality, most people are up and about by 7 or 8 o'clock, so we need to have that brightness then."
The Department of Justice said today that an EU Commission proposal to stop seasonal time adjustments from next year would have "particular implications for the island of Ireland," particularly in light of Brexit.
The Department said it conducted a wide-ranging public survey on this issue and added: "The results demonstrated that the overwhelming majority of respondents would not be in favour of any change that would result in two time zones on the island of Ireland, which would inevitably lead to increased difficulties for business and the general public."
Ireland is also concerned that the proposal could reduce synchronicity of time zones across Europe, resulting in "a 'patchwork' of time zones across the EU, thereby causing unnecessary confusion in the Single Market."
The Department of Justice said Ireland has supported a call for a full impact assessment of this proposal to be carried out, prior to any final decisions being made at EU level.