The time it takes to release money from pensions depends entirely on the pension type and the current timescales for your specific provider.
Just after pension freedoms began in April 2015, this took a long time. Now, however, most providers are actioning clients' requests within about 10 working days. If you are drawing taxable income in addition to tax-free cash, it would be worth checking with your pension provider if they have a specific payroll date that they pay taxable income out on as this may affect how long you have to wait for the money to be paid.
Your pension provider would also be able to let you know the administrative forms and process for releasing money from your pension, and any additional information that they may need from you to process the request. You may have to provide proof of your bank account or identification and it's always best to check with your pension provider so you understand what to expect. Be aware that withdrawing from your pension may affect your ability to save further into pensions if you are accessing taxable income and tax-free cash from this withdrawal.
Please also be mindful of the tax implications on the withdrawal that you are planning. Up to 25% of the pension fund can normally be drawn tax free, if you are only releasing tax free cash then you would not need to worry about the income tax implications. Your ability to save more into pensions in future would not be reduced. However, if you draw tax free cash and taxable income the provider may tax you on a higher rate, and you would have to reclaim any overpaid tax either through a self-assessment tax return or by completing a form on the government website https://www.gov.uk/claim-tax-refund/you-get-a-pension. A bit time consuming and bothersome!
I hope this helps