Open procedures are regimented in reg.27 of the Public Contracts Regulations 2015 (PCR2015), which transposes the rules in Art 27 of Directive 2014/24--once again, altering the order of its contents without substantive changes. The rules are quite straightforward (but not free from criticism, as Pedro has shown).
Firstly, given the open nature and the one-stage design of these procedures, any interested economic operator may submit a tender in response to a contract notice [reg.27(1) PCR2015], and the tender shall be accompanied by the information for qualitative selection that is requested by the contracting authority [reg.27(3) PCR2015].
Secondly, the general minimum time limit for the he receipt of tenders shall be 35 days from the date on which the contract notice was sent [reg.27(2) PCR2015], which can be reduced by 5 days the time limit for receipt of tenders where it accepts that tenders may be submitted by electronic means in accordance with reg.22 PCR2015 [reg.27(6) PCR2015].
Thirdly, this time limit can be reduced to 15 days in two cases: (a) where contracting authorities have published a prior information notice
which was not itself used as a means of calling for competition between 35 days and 12 months before the date on which the contract notice was sent, and included all the information required for the contract notice [reg.27(4) PCR2015]; or (b) where a state of urgency duly substantiated by the contracting authority renders impracticable the 35-day time limit [reg.27(5) PCR2015].
Consequently, the range of minimum time limits applicable to open procedures will be of 15-30-35 days, depending on the circumstances of the case [see Annex B of the Crown Commercial Service, A brief guide to the EU Public Contracts Directive (2014, updated Feb 2015)]. This does not mean that this is always or necessarily the adequate time span that contracting authorities should allow for tender preparation, and that time limit should be set in accordance with the principles of proportionality and competition [see reg.18 PCR2015].