June is the best time imho. However I won;t be going abroad this year. I do think it's right that vaccinated people should have to test before leaving and on arrival home unless/until it's proven they cannot transmit the disease asymptomatically (or have say <0.1% chance of doing do), hopefully it'll put more people off travelling out of the UK this year and risking coming into contact with other holidaymakers from countries without high levels of sequencing. The consequences for UK are just too high and foreign holidays can bounce back later in the year or in Spring 2022 or 2023 when it's safe for them to do so without prodding a surge in infections.
There's little chance even with green list people for whom a positive pre-departure test from a holiday location would prevent them getting home on time that they'll go on holiday abroad. There's just not enough control on what people do on holiday in countries where the main objective is sustaining their economies from tourism, whether responsible or not.... and in many cases it will be the latter.
I love Ibiza to bits and miss it a lot, but I'm dead against international travel right now. Once 70-80% of the population has had both doses of vaccine, and a further 2 weeks have passed since the last group had their second dose, then if the vaccines used are sufficiently effective against variants (i.e. Astrazeneca mainly in UK) I would be OK with allowing fully vaccinated travellers only to travel - and all others having to be tested and self isolate on return. But I would only travel personally once all testing is off the table I'm not going on holiday to worry about arranging PCR tests to get home and possibly getting stranded abroad, where's the fun in that
I think the majority of Brits will feel the same - and if it's enough of a risk to need PCR tests after 2 vaccine doses the subtext is we shouldn't be travelling on holiday abroad at all.