I am sure this information will be great use to politicos!
Tuesday, 20 March
Last day for publication of notice of election (London Mayor/GLA)
Start of regulated period for London Mayor, GLA constituency and independent GLA list candidates (for party GLA list candidates it starts when nomination papers submitted)
Thursday, 22 March
Last day for publication of notice of election (council elections Scotland)
Tuesday, 27 March
Last day for publication of notice of election (council elections England & Wales)
Wednesday, 28 March
Last day for submission of nomination papers (noon) (London Mayor/GLA)
Thursday, 29 March
Last day for submission of nomination papers (4pm) (council elections Scotland)
Last day for appointment of election agents (4pm) (council elections Scotland)
Friday, 30 March
Last day for publication of nominations (noon) (London Mayor/GLA)
Monday, 2 April
Last day for withdrawal of candidates (noon) (London Mayor/GLA)
Wednesday, 4 April
Last day for submission of nomination papers (noon) (council elections England & Wales)
Tuesday, 10 April
Last day for publication of nominations (noon) (council elections)
Wednesday, 11 April
Last day for withdrawal of candidates (noon) (council elections)
Last day for appointment of election agents (noon) (except for Scottish council elections)
Wednesday, 18 April
Last day to register to vote
Last day to apply for a new postal vote (5pm)
Last day to amend / cancel an existing postal vote arrangement (5pm)
Last day to amend / cancel an existing proxy vote arrangement (5pm)
Wednesday, 25 April
Last day to apply for a new proxy vote (5pm) – except for medical emergencies
Last day for publication of Notice of Poll (council elections)
Publication of Notice of Poll (London Mayor/GLA)
Thursday, 26 April
Last day for appointment of polling and counting agents
Thursday, 3 May
Polling Day: 7am – 10pm
Last day to apply for a new proxy vote on grounds of medical emergency (5pm)
Deadline for issuing replacement postal ballot papers (5pm)
Deadline for correcting electoral register due to clerical error or court appeal (9pm)
Thursday, 7 June
Last day for submission of election expense returns (if declaration was before midnight) (council elections)
Friday, 8 June
Last day for submission of election expense returns (if declaration was after midnight) (council elections)
Last day for submission of election expense returns (GLA constituency; assuming declaration on 4 May)
Friday, 13 July
Last day for submission of election expense returns (GLA list; assuming declaration on 4 May)
Last day for submission of election expense returns (London Mayor; assuming declaration on 4 May)
Thanks to ALDC, Electoral Commission and Mark Pack from whom I’ve extracted this information.